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HVAC terms are the specialized words and definitions used in the heating, ventilation, and air conditioning field. These terms help professionals, homeowners, and businesses understand system components, performance ratings, and energy performance.
Understanding HVAC terms helps you compare systems, fix problems, and talk with technicians. Knowing these key terms is important. It helps you make smart choices when buying a new unit or taking care of an old one.
Understanding HVAC terminology is essential for homeowners, technicians, and contractors. Knowing these HVAC terms and definitions helps in making informed decisions about heating, cooling, and ventilation systems.
A
AHRI (Air Conditioning, Heating, and Refrigeration Institute) – A certification body that make sure HVAC equipment meets efficiency and performance standards.
Air Handler – A component of an HVAC system that circulates conditioned air.
Annual Fuel Utilization Efficiency (AFUE) – A measure of a furnace’s efficiency in converting fuel into heat.
Air Conditioner (AC): A system or machine that cools and dehumidifies indoor air by removing heat and transferring it outside.
Air Conditioner (AC)
A system or machine that cools and dehumidifies indoor air by removing heat and transferring it outside.
Air changes per hour (ACH)
The number of times the air in a room is replaced with new air in one hour. Important for ventilation and indoor air quality.
Afue or annual fuel utilization efficiency
A measure of a furnace’s efficiency in converting fuel to energy over a year. Expressed as a percentage, higher AFUE ratings indicate greater efficiency.
Airflow
The movement of air through an HVAC system, measured in cubic feet per minute (CFM). Proper airflow is critical for system efficiency.
Air Balance
The process of adjusting an HVAC system to ensure even distribution of air throughout a building.
Ambient Temperature
The temperature of the surrounding air. In HVAC, it often refers to the outdoor temperature or the temperature of the air entering a system.
Air changes per hour
The number of times the air in a room is replaced with new air in one hour. Important for ventilation and indoor air quality.
AHU (Air Handling Unit)
A device used to regulate and circulate air as part of an HVAC system. It typically includes components like fans, filters, and heating/cooling coils.
Air-cooled system: Air cooling systems typically function by drawing cooler air from the environment and directing it over hot components
Air flow volume
Air flow volume is usually measured in cubic feet per minute (CFM). This shows how much air moves through a space in one minute.
Air Diffuser
A component that distributes conditioned air evenly into a room. It’s often part of the ductwork system.
Air Filter
A device used to remove dust, pollen, and other particles from the air before it circulates through the HVAC system.
Air Handler
The indoor part of an HVAC system that moves air throughout the home. It typically includes a blower, coils, and filters.
Air Purifier
A device that removes contaminants from the air to improve indoor air quality. Often used alongside HVAC systems.
Ambient Temperature
The temperature of the surrounding air. In HVAC, it often refers to the outdoor temperature or the temperature of the air entering a system.
ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers)
A group that sets the rules for HVAC systems and indoor air quality.
Automatic Damper
A device in ductwork adjusts airflow automatically. It helps different rooms stay comfortable and works more efficiently.
Axial Fan
A type of fan that moves air parallel to its axis. Commonly used in condenser units and exhaust systems.
Air Balance
The process of adjusting an HVAC system to ensure even distribution of air throughout a building.
Air Barrier
A material or system designed to prevent uncontrolled air leakage into or out of a building.
Air-Cooled Condenser
A type of condenser that uses air to remove heat from the refrigerant, commonly used in smaller HVAC systems.
Airflow Resistance
The opposition to airflow caused by filters, ducts, or other components in the HVAC system.
Air-Source Heat Pump
A type of heat pump that transfers heat between the indoor air and the outdoor air. It can provide both heating and cooling.
Air Tightness
A measure of how well a building or duct system prevents air leakage. Important for energy efficiency.
Air Vent
An opening in a duct or wall that allows air to enter or exit a space.
Air Volume
The amount of air flowing through an HVAC system, typically measured in cubic feet per minute (CFM).
Air Washer
A device that cleans and humidifies air by passing it through a water spray.
Ambient Air
The air surrounding a system or object, often referring to outdoor air.
Ammonia Refrigeration
A type of refrigeration system that uses ammonia as the refrigerant. Commonly used in industrial applications.
Anemometer
A device used to measure airflow velocity, often used in HVAC diagnostics.
Annual Maintenance: Regular servicing of an HVAC system to ensure optimal performance and longevity.
Anti-Short Cycle Device: A device that prevents an HVAC system from turning on and off too frequently, which can cause wear and tear.
Approach Temperature: The difference between the temperature of the refrigerant and the temperature of the air or water it is cooling.
Aquastat: A device used to control the temperature of water in a boiler or hydronic heating system.
B
Backflow Preventer: A device stops dirty water from flowing back into clean water. It’s often used in hydronic heating systems.
Balance Point: The outdoor temperature at which a heat pump’s heating capacity matches the heating needs of a building. Below this point, supplemental heating may be required.
Balancing Valve: This valve is key in hydronic systems. It controls water flow, helping to balance it. This ensures consistent heating or cooling across the system.
Barometric Damper
A device in combustion systems controls draft and airflow. It stops backdrafts and boosts efficiency.
Blower
A fan or motor-driven component in an HVAC system that circulates air through the ductwork and into the living spaces.
Blower Door Test
A diagnostic test used to measure the airtightness of a building and identify air leaks. It helps improve energy efficiency.
Boiler
A heating appliance that uses water or steam to distribute heat throughout a building. Common in hydronic heating systems.
Boiler Horsepower
A unit of measurement for the output capacity of a boiler. One boiler horsepower is equal to 33,475 BTU/h.
BTU (British Thermal Unit)
A unit of measurement for heat energy. One BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit.
BTU/h (BTU per Hour)
A measure of heating or cooling capacity over time. It indicates how much heat an HVAC system can add or remove in one hour.
Building Automation System (BAS)
A central system manages a building’s HVAC, lighting, security, and more. It helps optimize energy use and improve comfort.
Burner
A component in a furnace or boiler where fuel is burned to produce heat.
Burner Efficiency
A measure of how effectively a burner converts fuel into usable heat. Higher efficiency means less fuel waste.
Bypass Damper
A damper used in zoning systems to redirect excess airflow when only a few zones are active, preventing pressure imbalances.
Bypass Humidifier
A type of humidifier that uses the HVAC system’s airflow to add moisture to the air, bypassing the need for a separate fan.
Bypass Valve
A valve lets fluid, like water or refrigerant, skip some parts of a system. It’s often used for maintenance or to control pressure.
Backdrafting
Backdraft is a dangerous situation. Combustion gases get pulled back into a building instead of venting outside. This often happens due to negative pressure.
Baffle
A device used to direct or control the flow of air, water, or refrigerant within a system.
Baseboard Heater
A type of heating system installed along the baseboards of a room, often using electric resistance or hot water.
Biomass Heating
A heating system that uses organic materials (like wood pellets or agricultural waste) as fuel.
Blowdown
The process of removing concentrated impurities from a boiler by draining a portion of the water.
Boiler Feed Pump
A pump that supplies water to a boiler to maintain proper water levels.
Boiler Header
A pipe that distributes steam or hot water from a boiler to multiple outlets.
Boiler Relief Valve
A safety valve that releases pressure from a boiler if it exceeds safe levels.
Boiler Tube
A tube within a boiler that carries water or steam, transferring heat from the combustion process.
Breaker Panel
An electrical panel distributes power to an HVAC system and other devices. It has circuit breakers for safety.
Breathing Zone
The area in a room where occupants breathe, typically considered to be 3 to 6 feet above the floor.
Buffer Tank
A storage tank used in hydronic systems to store heated or chilled water, helping to balance supply and demand.
Building Envelope
The physical barrier in a building separates conditioned spaces from unconditioned ones. This includes walls, roofs, windows, and doors.
Burner Orifice
A small opening in a burner where fuel is released and mixed with air for combustion.
C
CAB (Clean Air Building)
A standard for buildings ensures high indoor air quality. It uses effective HVAC and filtration systems.
CAC (Central Air Conditioner)
A system that cools air at a central location and distributes it throughout a building via ductwork.
Calibration
Tweaking HVAC controls and sensors makes sure temperature, pressure, and humidity readings are right.
Capacity
The heating or cooling output of an HVAC system, typically measured in BTUs (British Thermal Units) or tons.
Capillary Tube
A narrow tube used in refrigeration systems to control the flow of refrigerant, often as part of the metering device.
Carbon Monoxide (CO)
A colorless, odorless gas produced by incomplete combustion. Proper HVAC maintenance is critical to prevent CO buildup.
Carbon Monoxide Detector
A safety device that alerts occupants to the presence of carbon monoxide, often integrated with HVAC systems.
Casing
The outer shell or housing of an HVAC component, such as a furnace or air handler.
Celsius (°C)
A temperature scale where water freezes at 0°C and boils at 100°C. Commonly used in HVAC for international standards.
Central Heating
A system that provides heat to an entire building from a single source, such as a furnace or boiler.
Centrifugal Fan
A type of fan that uses centrifugal force to move air, commonly used in HVAC systems for its efficiency and quiet operation.
CFM (Cubic Feet per Minute)
A measure of airflow volume, indicating how many cubic feet of air pass a point in one minute.
Charging
The process of adding refrigerant to an HVAC system to ensure proper operation.
Chiller
A device that removes heat from a liquid (usually water) via a vapor-compression or absorption cycle. Used in large cooling systems.
Chilled Water System
A type of air conditioning system that uses chilled water to cool air, often found in commercial buildings.
Circuit Breaker
A safety device that interrupts electrical flow in the event of an overload or short circuit, protecting HVAC equipment.
Cleanroom
A controlled environment with low levels of pollutants, often used in manufacturing or research. HVAC systems play a key role in maintaining air quality.
Coil
A component in an HVAC system that transfers heat. Common types include evaporator coils (cooling) and condenser coils (heat release).
Combustion
The process of burning fuel (e.g., natural gas, oil) to produce heat in a furnace or boiler.
Combustion Air
The air required for burning fuel in a furnace or boiler. Proper ventilation is essential for safe and efficient operation.
Compressor
The heart of a refrigeration or air conditioning system is the compressor. It pressurizes the refrigerant and moves it throughout the system.
Condensate
The water that forms when warm, humid air comes into contact with a cold surface, such as an evaporator coil.
Condensate Drain
A pipe or tube that removes condensate (water) from an HVAC system to prevent leaks or damage.
Condenser
A component in an air conditioning or refrigeration system that releases heat from the refrigerant, turning it from a gas to a liquid.
Condenser Coil
The part of the condenser where refrigerant releases heat to the outside air.
Condenser Fan
A fan that blows air over the condenser coil to dissipate heat.
Condensing Unit
The outdoor portion of an air conditioning system that houses the compressor, condenser coil, and fan.
Conduction
The transfer of heat through a material, such as walls or ducts, without the movement of the material itself.
Constant Air Volume (CAV)
A type of HVAC system that delivers a fixed amount of airflow, regardless of heating or cooling demand.
Control Panel
The interface that allows users to operate and monitor an HVAC system, often including thermostats and sensors.
Convection
The transfer of heat through the movement of fluids (air or water). In HVAC, it refers to how air circulates to heat or cool a space.
Cooling Load
The amount of heat energy that must be removed from a space to maintain a comfortable temperature.
Cooling Tower
A device used in large HVAC systems to remove heat from water by evaporating a small portion of it.
COP (Coefficient of Performance)
A measure of HVAC system efficiency, calculated as the ratio of heating or cooling output to energy input.
Crankcase Heater
A heater used in compressors to prevent refrigerant from migrating to the oil during off-cycles.
Cross Ventilation
The natural movement of air through a building, achieved by strategically placing windows or vents to create airflow.
Cubic Feet per Minute (CFM)
See CFM above.
Cycle
The complete operation of an HVAC system, including startup, runtime, and shutdown.
Cycling
The process of an HVAC system turning on and off to maintain a set temperature. Excessive cycling can reduce efficiency.
Cylinder
A container used to store refrigerant or other gases in an HVAC system.
D
Damper
A movable plate or valve within a duct system that regulates airflow. Dampers can be manual or automatic and are often used in zoning systems.
Damper Motor
A device that uses electricity or air pressure to control a damper’s position. This allows automatic regulation of airflow.
Datalogger
A device that tracks and records HVAC system performance over time. It measures temperature, humidity, and pressure.
Daylight Harvesting
A strategy that uses natural light cuts down on artificial lighting. It’s often combined with HVAC systems to boost energy efficiency.
Deadband
A temperature range where you don’t need to heat or cool. This helps save energy and reduces wear on the system.
Decibel (dB)
A unit of measurement for sound levels. HVAC systems are often rated for noise output in decibels.
Dehumidifier
A device that removes excess moisture from the air, improving comfort and preventing mold growth.
Delta T (ΔT)
The difference in temperature between two points, such as the air entering and exiting an HVAC system. Used to measure system performance.
Density
The mass per unit volume of air or another substance. Air density affects HVAC system performance and airflow calculations.
Desiccant
A substance used to absorb moisture from the air, often found in dehumidifiers or air dryers.
Design Temperature
The outdoor temperature used as a reference for sizing and designing HVAC systems, based on local climate data.
Dew Point
The temperature at which air becomes saturated with moisture and condensation begins to form. Important for humidity control.
Diffuser
A grille or vent that distributes conditioned air evenly into a room, often designed to minimize drafts.
Direct Expansion (DX) System
A type of air conditioning system where refrigerant cools air directly, as opposed to using chilled water.
Discharge Air
The air that exits an HVAC system after being heated, cooled, or filtered.
Discharge Pressure
The pressure of refrigerant as it leaves the compressor, a key factor in system performance.
Draft
The flow of air through a chimney, flue, or duct, often created by differences in air pressure.
Draft Hood
A device installed on a furnace or boiler to regulate draft and prevent backdrafting.
Drain Pan
A tray located beneath an evaporator coil to collect condensate and direct it to a drain.
Drier (or Filter-Drier)
A part of a refrigeration system that takes out moisture and dirt from the refrigerant.
Dry Bulb Temperature
The temperature of air measured without accounting for humidity, using a standard thermometer.
Dual-Fuel System
An HVAC system that combines a heat pump with a gas furnace, automatically switching between the two for optimal efficiency.
Duct
A passage or conduit used to deliver and return air in an HVAC system.
Duct Board
Insulated material used to construct ductwork, often made from fiberglass.
Duct Leakage
The loss of conditioned air through gaps or cracks in ductwork, reducing system efficiency.
Ductwork
The network of ducts that distributes air throughout a building.
Dust Spot Efficiency
A measure of an air filter’s ability to remove fine particles from the air, expressed as a percentage.
DX Coil (Direct Expansion Coil)
An evaporator coil used in a direct expansion system, where refrigerant cools air directly.
Dynamic Pressure
The pressure exerted by moving air within a duct or system, used in airflow calculations.
Damper Actuator
A motorized device that opens or closes dampers in response to signals from a control system.
Defrost Cycle
A process in heat pumps and refrigeration systems that removes ice buildup from the outdoor coil.
Degree Day
Heating or cooling demand is measured by the difference between the outdoor temperature and a base temperature, often 65°F.
Desuperheater
A device that recovers waste heat from a refrigeration or air conditioning system, often used to heat water.
Differential Pressure
The difference in pressure between two points in a system, often used to monitor filter condition or airflow.
Direct Digital Control (DDC)
A type of HVAC control system uses digital sensors and controllers. It optimizes performance.
Duct Static Pressure
Technicians measure pressure in a duct system to ensure good airflow and system performance.
Ductulator
A tool HVAC pros use to size ductwork. It considers airflow, friction, and more.
Ductless Mini-Split
A type of HVAC system that doesn’t need ductwork. It has an outdoor unit and one or more indoor air handlers.
Dust Collector
A device that removes dust and particles from the air. It’s commonly used in industrial HVAC systems.
Duty Cycle
The ratio of how long an HVAC system runs to its total cycle time shows its performance
E
EER (Energy Efficiency Ratio)
The cooling efficiency of an air conditioner is measured by the ratio of cooling output in BTUs to energy input in watts. This is calculated under specific conditions.
Economizer
An HVAC component that cools a building with outdoor air when conditions are right. This cuts down on mechanical cooling needs.
Effective Temperature
A measure of how warm or cool a person feels, taking into account temperature, humidity, and air movement.
Efficiency
A measure of how well an HVAC system converts energy into heating or cooling, often expressed as a percentage or ratio.
Electric Furnace
A heating system that uses electric resistance coils to generate heat, often used in areas with mild winters.
Electronically Commutated Motor (ECM)
A type of energy-efficient motor used in HVAC systems, known for its variable speed capabilities and low power consumption.
Emissions
Gases or particles released into the air as a byproduct of combustion in furnaces or boilers. Proper HVAC systems minimize harmful emissions.
Enthalpy
Total heat content of air is a thermodynamic property. It includes both sensible and latent heat.
Enthalpy Wheel
A device in energy recovery systems moves heat and moisture between incoming and outgoing air streams.
Environmental Control System
A system that controls temperature, humidity, and air quality in buildings. It’s often used in places like cleanrooms and data centers.
EPA (Environmental Protection Agency)
A U.S. agency makes rules for HVAC systems. This includes managing refrigerants and setting energy efficiency standards.
Equalizer Line
A small tube in a refrigeration system helps balance pressure between the high and low sides. It’s often found in thermostatic expansion valves.
Equipment Room
A dedicated space housing HVAC equipment, such as boilers, chillers, or air handlers.
ERV (Energy Recovery Ventilator)
A device that transfers heat and moisture between air streams. It boosts energy efficiency and improves indoor air quality.
Evaporator
A part of a refrigeration or air conditioning system, where refrigerant takes in heat and turns into gas. This process cools the air around it.
Evaporator Coil
The part of the evaporator where refrigerant absorbs heat from the air, typically located inside the air handler or furnace.
Exfiltration
The unintended leakage of air from a building, often through cracks or gaps in the building envelope.
Exhaust Air
Air that is expelled from a building, typically through vents or fans, after being used for ventilation or combustion.
Exhaust Fan
A fan that removes stale or contaminated air from a building, often used in kitchens, bathrooms, or industrial settings.
Expansion Valve
A part of a refrigeration system, this device controls how refrigerant flows into the evaporator. It lowers both the pressure and temperature.
External Static Pressure
The resistance to airflow caused by ductwork and other components outside the HVAC unit, measured in inches of water column (in. WC).
Extruded Fin
A type of heat exchanger fin made by extruding metal, often used in condenser or evaporator coils for improved heat transfer.
Energy Audit
An assessment of a building’s energy use, including HVAC systems, to identify opportunities for efficiency improvements.
Energy Recovery System
A system that captures waste energy (e.g., heat from exhaust air) and reuses it to reduce overall energy consumption.
Energy Star
A certification program by the EPA that identifies energy-efficient HVAC equipment and appliances.
Enthalpy Sensor
A device that measures the total heat content of air, used in HVAC controls to optimize system performance.
Evaporative Cooler
A cooling system that uses water evaporation to lower air temperature, often used in dry climates.
Exhaust Duct
A duct that carries stale or contaminated air out of a building.
Expansion Tank
A tank used in hydronic heating systems to accommodate the expansion and contraction of water as it heats and cools.
External Equalizer
A part of a thermostatic expansion valve helps control refrigerant flow and balance pressure.
Economizer Cycle
A control strategy uses outdoor air for cooling when temperatures drop below a set point. This cuts down on the need for mechanical cooling.
Efficiency Rating
HVAC systems are evaluated by their performance measures. Two key metrics are SEER (Seasonal Energy Efficiency Ratio) and AFUE (Annual Fuel Utilization Efficiency).
Electric Heat Pump
A heating and cooling system that transfers heat between the indoors and outdoors using electricity.
Energy Management System (EMS)
A computerized system that monitors and controls HVAC and other building systems to optimize energy use.
Evaporative Condenser
A condenser that cools refrigerant by using water evaporation. It’s commonly found in industrial settings.
Exhaust Vent
An opening or duct that allows air to exit a building, often connected to a fan or ventilation system.
Expansion Joint
A flexible connector in ductwork or piping that accommodates thermal expansion and contraction.
External Drive
A motor or drive system located outside the HVAC unit, often used in large commercial systems.
Energy Recovery Ventilator (ERV)
See ERV above.
Evaporator Fan
F
Fahrenheit (°F)
A temperature scale where water freezes at 32°F and boils at 212°F. Commonly used in HVAC systems in the United States.
Fan
A device with rotating blades that circulates air in an HVAC system. Types include centrifugal fans, axial fans, and propeller fans.
Fan Coil Unit (FCU)
A device that uses a fan and a coil to heat or cool air, often used in commercial or residential HVAC systems.
Fan Motor
The electric motor that drives the fan in an HVAC system, often variable-speed for improved efficiency.
Filter
A device that removes dust, pollen, and other particles from the air before it circulates through the HVAC system.
Filter Drier
A part of a refrigeration system that takes out moisture and dirt from the refrigerant.
Fire Damper
A safety device installed in ductwork that automatically closes to prevent the spread of fire and smoke.
Flame Sensor
A safety device in a furnace that detects whether the burner is lit. If no flame is detected, it shuts off the gas supply.
Flue
A pipe or duct that exhausts combustion gases from a furnace, boiler, or water heater to the outdoors.
Flue Gas
Exhaust gases come from burning fuel in a furnace or boiler. They usually contain carbon dioxide, water vapor, and nitrogen.
Flue Liner
A protective lining inside a flue that prevents corrosion and improves efficiency.
Forced Air System
An HVAC system that uses a fan to distribute heated or cooled air through ductwork.
Free Cooling
A strategy that uses outdoor air for cooling when temperatures are low enough, reducing the need for mechanical cooling.
Freeze Stat
A safety device that shuts off an HVAC system if the evaporator coil temperature drops too low, preventing freezing and damage.
Fresh Air Intake
A duct or vent that brings outdoor air into an HVAC system to improve ventilation and indoor air quality.
Frost Control
A feature in heat pumps and air conditioners that prevents frost buildup on the outdoor coil during cold weather.
Fuel Efficiency
AFUE stands for Annual Fuel Utilization Efficiency. It measures how well a furnace or boiler turns fuel into heat.
Furnace
A heating system generates heat using combustion or electric resistance. Then, it distributes the heat through ductwork.
Fuse
A safety device that interrupts electrical flow in the event of an overload, protecting HVAC equipment.
Face Velocity
The speed of air passing through a filter or coil, measured in feet per minute (FPM).
Fan Curve
A graph that shows the relationship between airflow and pressure in a fan, used for system design and troubleshooting.
Fan Laws
How changes in fan speed, airflow, and pressure impact performance.
Fan Power
The amount of energy consumed by a fan, often measured in watts or horsepower.
Fan Static Pressure
The pressure a fan must overcome to move air through a system, measured in inches of water column (in. WC).
Filter Efficiency
A measure of how well an air filter removes particles from the air, often expressed as MERV (Minimum Efficiency Reporting Value).
Firebox
The chamber in a furnace or boiler where fuel is burned to produce heat.
Flame Rollout
A dangerous situation occurs when flames leave the combustion chamber. This often happens due to blocked flues or poor airflow.
Flame Retention Burner
A burner designed to keep a steady flame. It boosts combustion efficiency and cuts down emissions.
Floodback
A situation in a refrigeration system occurs when liquid refrigerant returns to the compressor. This can cause damage.
Flow Rate
The volume of air or water moving through an HVAC system, often measured in cubic feet per minute (CFM) or gallons per minute (GPM).
Flue Damper
A device that regulates airflow in a flue, improving efficiency and preventing heat loss when the system is off.
Flue Pipe
A pipe that carries combustion gases from a furnace or boiler to the outdoors.
Foam Insulation
A type of insulation used in ductwork or building envelopes to reduce heat transfer and improve energy efficiency.
Foot Candle
A unit of measurement for light intensity, sometimes used in HVAC design to assess the impact of lighting on cooling loads.
Four-Pipe System
A type of HVAC system has separate pipes for heating and cooling. This setup lets different zones be heated and cooled at the same time.
Freeze Protection
Measures taken to prevent water in pipes or HVAC components from freezing, such as insulation or heat tracing.
Frequency Drive
A device that controls the speed of a motor, often used in HVAC systems to improve energy efficiency.
Friction Loss
The loss of pressure in a duct or pipe due to resistance from walls or fittings.
Frost Coil
A coil used in air handling units to preheat outdoor air and prevent frost buildup during cold weather.
Full Load
The maximum heating or cooling capacity required by a building under extreme conditions, used for system sizing.
G
Gage Pressure
The pressure of a fluid (such as refrigerant) measured relative to atmospheric pressure, often expressed in psi (pounds per square inch).
Gas Furnace
A heating system that uses natural gas or propane to generate heat, which is then distributed through ductwork.
Gas Valve
A device that controls the flow of gas to a furnace or boiler, ensuring safe and efficient operation.
Gauge
A device used to measure pressure, temperature, or other variables in an HVAC system.
Gauge Manifold
A tool used by HVAC technicians to measure high- and low-side pressures in a refrigeration system.
Geothermal Heat Pump
A type of heat pump that uses the earth’s constant temperature as a heat source or sink, offering high energy efficiency.
Globe Valve
A type of valve used to regulate fluid flow in HVAC systems, known for its precise control.
Grille
A decorative cover for an air vent or return air opening, often designed to blend with the building’s interior.
Ground Source Heat Pump
Another term for a geothermal heat pump, which uses the ground as a heat exchange medium.
GPM (Gallons Per Minute)
A measure of water flow rate, often used in hydronic heating or cooling systems.
Gravity Ventilation
A natural ventilation method that relies on the buoyancy of warm air to create airflow, without mechanical fans.
Green Building
A building built to reduce environmental impact. It often uses energy-efficient HVAC systems.
Greenhouse Gas (GHG)
Gases that contribute to global warming, such as carbon dioxide (CO2). HVAC systems can reduce GHG emissions through energy efficiency.
Grid
A framework or structure used to support ductwork, piping, or other HVAC components.
Grille Diffuser
A combination of a grille and diffuser that distributes air evenly while blending with the room’s decor.
Ground Loop
A series of pipes buried underground that transfer heat to or from a geothermal heat pump system.
Grounded Conductor
An electrical conductor that is intentionally connected to the ground for safety, often used in HVAC systems.
Grounded Outlet
An electrical outlet with a grounding connection, required for safe operation of HVAC equipment.
Grounding
The process of connecting electrical equipment to the earth to prevent electrical shock or damage.
Gun-Type Burner
A type of burner used in oil-fired furnaces or boilers, known for its high efficiency and compact design.
Gasket
A seal used to prevent leaks between two surfaces, such as in ductwork or piping connections.
Gas Detector
A device that detects the presence of combustible or toxic gases, often used in HVAC systems for safety.
Gas Pressure Regulator
A device that maintains a consistent gas pressure in a furnace or boiler, ensuring safe and efficient operation.
Gas Piping
Pipes that transport natural gas or propane to HVAC equipment, such as furnaces or boilers.
Gas Burner
A component in a furnace or boiler where gas is mixed with air and ignited to produce heat.
Gas Leak Detector
A tool used to identify leaks in gas piping or HVAC equipment, ensuring safety and preventing energy waste.
Gas Meter
A device that measures the volume of gas consumed by an HVAC system or other appliances.
Gas Vent
A pipe or duct that exhausts combustion gases from a furnace or boiler to the outdoors.
Gauge Glass
A transparent tube or window used to monitor the water level in a boiler.
Gauge Pressure Sensor
A device that measures pressure relative to atmospheric pressure, often used in HVAC controls.
Gauge Set
A set of gauges used by HVAC technicians to measure pressure and temperature in refrigeration systems.
General Ventilation
A system that provides fresh air to an entire building, as opposed to localized ventilation.
Glazing
The glass or transparent material in windows, which affects heat transfer and cooling loads.
Glycol
A fluid used in hydronic heating or cooling systems to prevent freezing and corrosion.
Grade
The slope or angle of a pipe or duct, often used to ensure proper drainage or airflow.
Gravity Heating System
A heating system that relies on the natural circulation of warm air or water, without mechanical pumps or fans.
Grease Duct
A duct designed to carry grease-laden air from commercial kitchens to an exhaust fan or filter.
Grease Filter
A filter used in kitchen exhaust systems to remove grease from the air before it enters the ductwork.
Green HVAC
HVAC systems aim to reduce environmental harm. They do this by being energy efficient, using renewable energy, or following sustainable practices.
Ground Fault Circuit Interrupter (GFCI)
A safety device that shuts off electrical power in the event of a ground fault, often used in HVAC systems near water sources.
H
Heat
A form of energy that is transferred between systems or objects due to a temperature difference. HVAC systems manage heat to maintain comfort.
Heat Exchanger
A device that transfers heat between two fluids (such as air and refrigerant) without mixing them. Common in furnaces, boilers, and air conditioners.
Heat Gain
The increase in heat within a space, often caused by sunlight, appliances, or occupants. HVAC systems must remove heat gain to maintain comfort.
Heat Loss
The decrease in heat within a space, often due to poor insulation or cold outdoor temperatures. HVAC systems must compensate for heat loss.
Heat Pump
A system that transfers heat between the indoors and outdoors, providing both heating and cooling. Types include air-source and ground-source heat pumps.
Heat Recovery Ventilator (HRV)
A device that transfers heat between incoming and outgoing air. It boosts energy efficiency and improves indoor air quality.
Heat Transfer
The movement of heat from one place to another, occurring through conduction, convection, or radiation.
Heating Coil
A coil in an HVAC system that heats air as it passes over it, often using hot water, steam, or electric resistance.
Heating Load
Heat energy is needed to keep indoor spaces comfy. This amount depends on outdoor conditions and the building’s features.
Heating Seasonal Performance Factor (HSPF)
A measure of a heat pump’s heating efficiency over a season, calculated as the ratio of heat output to energy input.
High-Efficiency Particulate Air (HEPA) Filter
A type of air filter that removes at least 99.97% of airborne particles, including dust, pollen, and bacteria.
High-Pressure Cutoff Switch
A safety device that shuts off a refrigeration or air conditioning system if the pressure exceeds a safe level.
High-Side Pressure
The refrigerant pressure in the condenser side is usually higher than in the evaporator side.
Horsepower (HP)
A unit of power used to describe the capacity of motors, compressors, and other HVAC components.
Hot Water Boiler
A heating system that uses water to distribute heat, often through radiators or baseboard heaters.
Humidifier
A device that adds moisture to the air, improving comfort and preventing issues like dry skin or static electricity.
Humidistat
A device that measures and controls humidity levels, often integrated with an HVAC system.
Humidity
The amount of water vapor in the air. HVAC systems manage humidity to ensure comfort and prevent mold growth.
HVAC (Heating, Ventilation, and Air Conditioning)
The technology and systems used to control indoor temperature, humidity, and air quality.
Hydronic Heating
A heating system transfers heat using water or another liquid. It often works through radiators, baseboard heaters, or radiant floor systems.
Hydronic Radiant Heating
A type of hydronic heating where hot water circulates through pipes embedded in floors, walls, or ceilings to provide even heat.
Hydrostatic Pressure
The pressure exerted by a fluid at rest, often considered in hydronic heating systems.
Hygrometer
A device used to measure humidity levels in the air.
Hygroscopic
A material’s ability to absorb moisture from the air, often considered in HVAC design for insulation or ductwork.
Heat Anticipator
A component in a thermostat that reduces temperature swings by anticipating heating or cooling needs.
Heat Defrost
A method used in heat pumps to remove ice buildup from the outdoor coil during cold weather.
Heat Island Effect
Urban heat islands are when cities are much warmer than nearby rural areas. This can impact HVAC cooling needs.
Heat Recovery
The process of capturing waste heat from exhaust air or other sources and reusing it to improve energy efficiency.
Heat Sink
A component or material that absorbs and dissipates heat, often used in HVAC equipment to prevent overheating.
Heat Strip
An electric resistance heating element used in heat pumps or air handlers to provide supplemental heat.
Heat Wheel
A rotating device in energy recovery systems moves heat and moisture between incoming and outgoing air streams.
High-Velocity System
An HVAC system that uses smaller ducts and higher airflow speeds to deliver conditioned air, often used in retrofits.
Horizontal Flow
A type of air handling unit where air flows horizontally through the unit, often used in tight spaces.
Hot Gas Bypass
A method in refrigeration systems stops evaporator coils from freezing. It does this by redirecting hot refrigerant gas.
Hot Gas Defrost
A defrost method in refrigeration systems that uses hot refrigerant gas to melt ice buildup on the evaporator coil.
Hot Gas Reheat
In air conditioning, hot refrigerant gas reheats air. This process helps to reduce humidity.
Hot Surface Ignition
A type of ignition system in furnaces that uses an electrically heated element to ignite the gas burner.
Hot Water Heating System
See Hydronic Heating above.
Humidity Ratio
The ratio of the mass of water vapor to the mass of dry air in a mixture, used in psychrometric calculations.
HVAC Zoning
A system splits a building into zones. This setup lets you control the temperature in each area. As a result, it boosts comfort and efficiency.
I
IAQ (Indoor Air Quality)
The quality of air inside a building, which affects occupant health and comfort. HVAC systems play a key role in maintaining good IAQ.
Ice Bank
A system that stores ice produced during off-peak hours for use in cooling during peak demand periods.
Ice Maker
An ice-making refrigeration unit is often part of HVAC systems. It can be used in both commercial and residential settings.
Ignition System
The component in a furnace or boiler that ignites the fuel to produce heat. Types include hot surface ignition and intermittent pilot.
Immersion Heater
A heating element installed directly in a liquid, often used in boilers or water tanks.
Impeller
A rotating component in a pump or fan that moves fluid or air by creating centrifugal force.
Inch of Water Column (in. WC)
A unit of pressure commonly used in HVAC to measure airflow resistance or gas pressure.
Indoor Coil
The evaporator coil in an air conditioning or heat pump system, located inside the air handler or furnace.
Indoor Unit
The portion of an HVAC system located inside a building, typically including the air handler, evaporator coil, and filter.
Infiltration
Outdoor air can leak into a building through cracks, gaps, or openings. This leakage can impact heating and cooling loads.
Infrared Heater
A heating device that uses infrared radiation to warm objects and people directly, rather than heating the air.
Inlet
The opening or duct where air enters an HVAC system or component.
Inlet Vane
A device used to control airflow into a fan or blower, improving efficiency and reducing energy consumption.
Insulation
Insulation reduces heat transfer in ductwork, pipes, or building envelopes. This helps improve energy efficiency.
Intercooler
A device used in multi-stage compression systems to cool air between stages, improving efficiency.
Inverter Compressor
A type of compressor that adjusts its speed to match cooling or heating demand, improving energy efficiency and comfort.
Isolation Valve
A valve used to shut off flow to a specific component or section of an HVAC system for maintenance or repair.
Isolation Mount
A vibration-dampening mount used to reduce noise and vibration from HVAC equipment.
Isentropic Efficiency
A measure of how efficiently a compressor or turbine converts energy, often used in HVAC system design.
Isothermal Process
A thermodynamic process at a constant temperature is important in HVAC system analysis.
Indirect Evaporative Cooling
A cooling method that uses evaporation to cool air without adding moisture, often used in dry climates.
Indirect-Fired Heater
A heating system where combustion gases do not come into contact with the air being heated, improving safety and air quality.
Indoor Air Handler
See Indoor Unit above.
Indoor Design Temperature
The target temperature for indoor spaces, used in HVAC system design and load calculations.
Induced Draft
A type of furnace or boiler that uses a fan to pull combustion gases through the heat exchanger and out the flue.
Infrared Thermometer
A device used to measure surface temperatures from a distance, often used in HVAC diagnostics.
Inlet Air Temperature
The temperature of air entering an HVAC system or component, used in performance calculations.
Inlet Guide Vane
A device used to control the angle of airflow entering a fan or compressor, improving efficiency.
Insulated Duct
Ductwork covered with insulation to reduce heat loss or gain and improve energy efficiency.
Insulated Glazing
Windows with several glass panes filled with insulating gas help cut heat transfer and boost energy efficiency.
Integrated Control System
A centralized system that controls multiple building systems, including HVAC, lighting, and security.
Interlock
A safety feature that prevents HVAC equipment from operating under unsafe conditions, such as a blocked flue.
Internal Heat Gain
Heat created by people, lights, appliances, or equipment in a building impacts cooling needs.
Inverter-Driven Compressor
See Inverter Compressor above.
Ionization
A process used in some air purifiers to remove particles from the air by charging them electrically.
Isolation Damper
A damper used to isolate a section of ductwork for maintenance or to prevent airflow between zones.
Isolation Gasket
A gasket used to prevent vibration and noise transmission between HVAC components.
Isolation Transformer
A transformer used to isolate HVAC equipment from electrical noise or voltage fluctuations.
Isolation Valve
See Isolation Valve above.
Isothermal Humidifier
A humidifier adds moisture to the air. It does this without changing the temperature. It’s often used in precise settings.
J
Jacket
The outer casing of a boiler or furnace, often insulated to reduce heat loss and improve efficiency.
Jacket Loss
The heat lost through the outer casing (jacket) of a boiler or furnace, which reduces overall efficiency.
Joule
A unit of energy in the International System of Units (SI). In HVAC, it’s sometimes used to measure heat energy or work done.
Junction Box
A box that holds electrical connections. It’s often used in HVAC systems to link wiring for motors, controls, or other parts.
Junction Duct
A section of ductwork where multiple ducts connect, often used to distribute airflow to different zones or rooms.
Jet Pump
A type of pump used in some HVAC systems to move fluids, such as water or refrigerant, by creating a high-velocity jet.
Jockey Pump
A small pump in hydronic heating systems keeps the pressure steady. It also circulates water when demand is low.
Joule-Thomson Effect
A thermodynamic process where a gas cools or heats as it expands or compresses. This principle is sometimes applied in refrigeration systems.
Jumper Wire
A short wire used to bypass a component or complete an electrical circuit, often used in HVAC controls or diagnostics.
Jacketed Valve
A valve with an insulated or heated outer casing, often used in steam or high-temperature systems to prevent heat loss.
Jet Nozzle
A device used to control the flow and direction of fluids, such as refrigerant or water, in HVAC systems.
Joint Compound
A material used to seal joints in ductwork or piping, preventing air or fluid leaks.
Joggle
A bend or offset in sheet metal, often used in ductwork fabrication to create tight seals or connections.
Junction Point
A location in an HVAC system where multiple components, ducts, or pipes connect.
J-Type Thermocouple
A type of temperature sensor used in HVAC systems to measure high temperatures, often in furnaces or boilers.
Jacketed Heat Exchanger
A heat exchanger with an insulated or heated outer casing, used to maintain temperature and improve efficiency.
Jet Stream
A high-velocity flow of air or fluid, sometimes referenced in HVAC design for airflow optimization.
Jig
A tool or fixture used in HVAC fabrication to hold components in place during assembly or installation.
J-Box
A shorthand term for a junction box, commonly used in HVAC electrical systems.
Joggle Plate
A metal plate with a bend or offset, used in ductwork to create a secure connection between sections.
K
Kelvin (K)
A unit of temperature in the International System of Units (SI). It is often used in scientific HVAC calculations, where 0 K is absolute zero.
Kilowatt (kW)
A unit of power equal to 1,000 watts. HVAC systems, especially electric heaters and heat pumps, are often rated in kilowatts.
Kilowatt-Hour (kWh)
A unit of energy representing the amount of energy consumed by a 1-kilowatt device operating for one hour. Used to measure HVAC energy usage.
K-Factor
A value used in ductwork design to account for pressure losses due to fittings, bends, and other obstructions.
Kick Space Heater
A small, low-profile heater installed under cabinets or in tight spaces, often used in kitchens or bathrooms.
Kilocalorie (kcal)
A unit of heat energy, often used in older HVAC systems or international contexts. 1 kcal is the amount of heat needed to raise 1 kg of water by 1°C.
Kinematic Viscosity
A measure of a fluid’s resistance to flow under gravity, often considered in HVAC systems for refrigerant or oil selection.
Kitchen Hood
A ventilation system sits above cooking appliances. It removes heat, smoke, and greasy air from both commercial and residential kitchens.
Kitchen Exhaust Fan
A fan used in conjunction with a kitchen hood to exhaust air to the outdoors, maintaining indoor air quality.
Knockout
A pre-cut section in an electrical box or HVAC component that can be removed to allow wiring or piping connections.
kPa (Kilopascal)
A unit of pressure commonly used in HVAC systems, especially in countries using the metric system. 1 kPa = 1,000 Pascals.
kW/Ton
A measure of cooling efficiency, representing the power input (in kilowatts) required to produce one ton of cooling.
Kerosene Heater
A type of heater that burns kerosene fuel to produce heat, often used as a supplemental heating source.
Keyhole Saw
A small, handheld saw used in HVAC installation to cut holes in walls or ceilings for ductwork or piping.
Kinetic Energy Recovery System
A system that captures and reuses energy from moving air or fluids, sometimes applied in HVAC for energy efficiency.
Knurled Nut
A nut with a textured surface for easy gripping, often used in HVAC assembly or maintenance.
K-Type Thermocouple
A type of temperature sensor commonly used in HVAC systems to measure high temperatures, such as in furnaces or boilers.
Kick Plate
A protective plate installed at the base of doors or walls to prevent damage from foot traffic or equipment.
Kilogram (kg)
A unit of mass used in HVAC for measuring refrigerant quantities or system components.
Kilopascal Meter (kPa·m)
A unit used to measure pressure drop in ductwork or piping systems.
Kitchen Makeup Air Unit
A system that brings in outdoor air to replace air pulled out by kitchen hoods. This keeps ventilation and pressure balanced.
Knockout Plug
A removable plug used to seal unused openings in HVAC equipment or ductwork.
Kerosene Furnace
A furnace that burns kerosene fuel to produce heat, often used in areas without access to natural gas.
K-Factor Ductwork
Ductwork designed with specific pressure loss characteristics, often used in custom HVAC installations.
Kilovolt-Ampere (kVA)
A unit of electrical power used to rate transformers or other HVAC electrical components.
Kinetic Heating
A process where heat is generated by the movement of air or fluids, sometimes used in specialized HVAC applications.
Knockout Punch
A tool used to create holes in sheet metal or ductwork for piping or wiring connections.
Kerosene Boiler
A kerosene boiler is commonly used in homes and small businesses.
Kilowatt Meter
A device used to measure the electrical power consumption of HVAC equipment.
K-Value (Thermal Conductivity)
Thermal conductivity shows how well a material can conduct heat. It’s commonly used in insulation and heat exchanger design.
L
Latent Heat
The heat energy absorbed or released during a phase change (e.g., water vapor condensing into liquid), without a change in temperature. Important in cooling and dehumidification.
Latent Cooling Load
The cooling needed to take moisture out of the air is different from the sensible cooling load, which is about lowering the temperature.
Leak Detector
A device used to locate leaks in refrigerant lines, ductwork, or piping.
Life Cycle Cost
The total cost of owning and running an HVAC system includes installation, maintenance, and energy costs over its lifetime.
Load Calculation
Finding out how much heating or cooling a building needs depends on its size, insulation, and climate.
Louvers
Slatted vents or grilles that allow air to pass through while blocking rain, debris, or direct sunlight.
Lowboy Furnace
A compact, low-profile furnace designed for installation in spaces with limited vertical clearance.
Low-Pressure Cutoff Switch
A safety device that shuts off an HVAC system if the pressure drops below a safe level, often used in refrigeration systems.
Low-Side Pressure
The pressure of refrigerant in the evaporator side of a refrigeration system, typically lower than the condenser side.
Lubricant
A substance used to reduce friction and wear in HVAC components, such as compressors or motors.
Liquid Line
The pipe in a refrigeration system that carries liquid refrigerant from the condenser to the expansion valve.
Liquid Receiver
A storage tank in a refrigeration system that holds excess liquid refrigerant.
Load Shedding
A strategy to cut energy use during peak times is to turn off non-essential HVAC equipment temporarily.
Laminar Flow
A smooth, orderly flow of air with minimal turbulence, often desired in cleanrooms or laboratories.
Line Set
The pair of copper tubes (suction and liquid lines) that connect the indoor and outdoor units of a split HVAC system.
Load Profile
A graph or chart showing the heating or cooling demand of a building over time, used for system design and optimization.
Louvered Damper
A damper with slatted blades that can be adjusted to control airflow.
Low-E (Low Emissivity) Glass
A type of glass with a special coating that reduces heat transfer, improving energy efficiency in windows.
Low-Flow Fixture
A plumbing fixture designed to use less water, reducing the load on water heaters and boilers.
Low-NOx Burner
A burner that cuts nitrogen oxide (NOx) emissions helps improve air quality. It also ensures compliance with environmental rules.
Liquid Refrigerant
Refrigerant in its liquid state, typically found in the condenser and liquid line of a refrigeration system.
Liquid Subcooling
The process of cooling liquid refrigerant below its saturation temperature, improving system efficiency.
Load Factor
The ratio of average load to peak load, used to assess the efficiency of an HVAC system.
Load Management
Controlling HVAC equipment helps cut energy use during peak demand times.
Local Exhaust Ventilation (LEV)
A system that captures and removes contaminants at their source, often used in industrial or laboratory settings.
Lockout
A safety feature that prevents an HVAC system from operating after a fault or failure until it is manually reset.
Longitudinal Seam
The seam running along the length of a duct or pipe, often sealed to prevent leaks.
Low Ambient Control
A feature in air conditioning systems that allows operation in low outdoor temperatures, often used in heat pumps.
Low-Pressure Chiller
A chiller designed to operate at lower pressures, often using water as a refrigerant.
Low-Voltage Wiring
Electrical wiring that carries less than 50 volts, commonly used in HVAC controls and thermostats.
LPG (Liquefied Petroleum Gas)
A fuel source used in some HVAC systems, such as furnaces or boilers.
LTHW (Low-Temperature Hot Water)
A hydronic heating system that uses water at lower temperatures, improving energy efficiency.
Laminar Airflow
A controlled, unidirectional flow of air, often used in cleanrooms or surgical suites.
Latent Heat of Fusion
The heat energy absorbed or released when a substance changes between solid and liquid states.
Latent Heat of Vaporization
The heat energy absorbed or released when a substance changes between liquid and gas states.
Leakage Rate
The rate at which air or refrigerant escapes from a system, often measured in cubic feet per minute (CFM) or pounds per year.
Limit Switch
A safety device that shuts off an HVAC system if temperatures or pressures exceed safe levels.
Liquid Indicator
A sight glass or device used to monitor the level or condition of liquid refrigerant in a system.
Load Shed Thermostat
A thermostat cuts HVAC energy use during peak times. It’s usually part of a demand response program.
Louvered Vent
A vent with adjustable slats to control the direction and flow of air.
M
MAU (Makeup Air Unit)
A system that brings in fresh outdoor air. It replaces the air that ventilation systems exhaust. This helps keep the right pressure balance and good indoor air quality.
Manifold
A pipe or chamber with multiple outlets for distributing or collecting fluid, often used in hydronic heating systems.
Manometer
A device used to measure pressure, often in ductwork or gas lines, using a column of liquid (e.g., water or mercury).
Manual J Calculation
ACCA (Air Conditioning Contractors of America) created a standard way to calculate heating and cooling loads for homes.
Manual D
A duct design standard developed by ACCA for sizing and designing ductwork in residential HVAC systems.
Manual S
A standard for selecting and sizing HVAC equipment based on load calculations and system design.
Manual T
A standard for designing and selecting air distribution components, such as grilles and diffusers.
MERV (Minimum Efficiency Reporting Value)
A rating system for air filters that measures their ability to capture particles of different sizes. Higher MERV ratings indicate better filtration.
Microchannel Coil
A type of heat exchanger with small, flat tubes and fins, used in condensers and evaporators for improved efficiency.
Mini-Split System
A ductless HVAC system with an outdoor compressor/condenser and one or more indoor air handlers, often used in retrofits or small spaces.
Modulating Burner
A burner that adjusts its output to match heating demand, improving efficiency and comfort.
Modulating Valve
A valve that adjusts the flow of fluid (water, refrigerant, or gas) to maintain precise control over system performance.
Moisture Barrier
A material used to prevent moisture from entering or escaping a building envelope, often used in insulation or ductwork.
Motor
An electric device changes electrical energy into mechanical energy. It powers fans, compressors, and pumps in HVAC systems.
Motorized Damper
A damper controlled by an electric motor, often used in zoning systems to regulate airflow.
Multizone System
An HVAC system that allows independent temperature control in different zones or areas of a building.
Makeup Air
Outdoor air comes into a building to replace the air that ventilation systems exhaust. This helps maintain the right pressure balance.
Manifold Gauge Set
A tool used by HVAC technicians to measure pressure and temperature in refrigeration systems.
Mass Flow Rate
The amount of air or fluid moving through a system, often measured in pounds per hour or kilograms per second.
Mechanical Ventilation
The use of fans or other mechanical systems to provide fresh air and remove stale air from a building.
Metering Device
A part of a refrigeration system controls refrigerant flow into the evaporator. This includes devices like a thermostatic expansion valve (TXV) or a capillary tube.
Microbial Growth
The growth of mold, bacteria, or other microorganisms in HVAC systems, often due to moisture or poor maintenance.
Millimeter of Mercury (mmHg)
A unit of pressure, often used in HVAC for measuring vacuum levels or gas pressure.
Mixed Air
A combination of outdoor air and recirculated air in an HVAC system, often used to improve energy efficiency.
Modulating Heat Pump
A heat pump that adjusts its output to match heating or cooling demand, improving efficiency and comfort.
Moisture Load
Moisture in indoor air comes from people, activities, or outside air. This affects humidity levels.
Monobloc Heat Pump
A type of air-source heat pump where all components are housed in a single outdoor unit.
Motor Efficiency
Efficiency shows how well a motor turns electrical energy into mechanical energy. It is usually given as a percentage.
Mullion Heater
A heating element is placed in the mullion, the vertical divider of a refrigerator or freezer. This helps stop condensation.
Multi-Stage System
An HVAC system with multiple levels of heating or cooling output, allowing it to operate more efficiently at partial loads.
Muntin Heater
A heating element is placed in the muntin, the horizontal divider of a refrigerator or freezer. It helps stop condensation.
Mixing Box
A part of an air handling unit mixes outdoor air with recirculated air. This blending helps reach the right temperature and humidity.
Mixing Valve
A valve that blends hot and cold water to achieve a desired temperature, often used in hydronic heating systems.
Moisture Sensor
A device that measures humidity levels in the air or moisture content in materials, often used in HVAC controls.
Motor Starter
A device used to control the operation of an electric motor, often including overload protection.
Mullion
A vertical divider sits between windows or doors. It may have heaters to stop condensation.
Muntin
A horizontal divider between windows or doors. It may have heaters to stop condensation.
Muffler
A device used to reduce noise in HVAC systems, often installed in ductwork or near compressors.
Mullion Heater
See Mullion Heater above.
Muntin Heater
See Muntin Heater above.
N
Natural Convection
The movement of air or fluid due to temperature differences, without the use of fans or pumps. Often used in passive heating or cooling systems.
Natural Gas
A fossil fuel commonly used in furnaces, boilers, and water heaters for heating. It is a clean-burning and efficient energy source.
Natural Ventilation
The process of supplying fresh air to a building through windows, vents, or other openings without mechanical systems.
Needle Valve
A valve with a small, precise opening used to control the flow of refrigerant or other fluids in HVAC systems.
Net Cooling Capacity
The actual cooling capacity of an HVAC system after accounting for losses such as fan power or heat gain.
Net Positive Suction Head (NPSH)
A measure of the pressure available at the inlet of a pump, ensuring proper operation and preventing cavitation.
Net Refrigeration Effect
The amount of heat absorbed by the refrigerant in the evaporator, representing the useful cooling capacity of the system.
Net Zero Energy Building
A building that makes as much energy as it uses. This is often done with energy-efficient HVAC systems and renewable energy sources.
Neutral Pressure
A condition where the air pressure inside a building matches the outdoor air pressure. This stops air from coming in or going out.
Night Purge
A strategy that uses cool nighttime air to ventilate and cool a building, reducing the need for mechanical cooling during the day.
Nitrogen Purging
Using nitrogen gas cleans contaminants or moisture from HVAC systems. This is important during installation or repair.
Noise Criterion (NC)
A rating system used to measure and evaluate noise levels in HVAC systems, ensuring occupant comfort.
Non-Condensable Gas
A gas that doesn’t condense in normal conditions can lead to inefficiencies in refrigeration systems.
Non-Ferrous
Materials that do not contain iron, such as copper or aluminum, often used in HVAC components to prevent corrosion.
Non-Return Valve
A valve that allows fluid to flow in only one direction, preventing backflow in HVAC systems.
Normal Operating Conditions
HVAC systems are designed to work under standard conditions. These include temperature, pressure, and load.
Nozzle
A device used to control the flow or direction of air, water, or refrigerant in HVAC systems.
NTC Thermistor
A type of temperature sensor with a negative temperature coefficient, often used in HVAC controls.
Nuisance Tripping
The unwanted shutdown of an HVAC system due to minor faults or false alarms, often caused by improper settings or faulty components.
NEMA (National Electrical Manufacturers Association)
An organization that sets standards for electrical equipment, including HVAC motors and controls.
NEMA Enclosure Rating
A rating system that defines the level of protection provided by electrical enclosures, such as those used in HVAC systems.
Net Heating Capacity
The actual heating capacity of an HVAC system after accounting for losses such as fan power or heat loss.
Net Zero HVAC
An HVAC system aims for net zero energy use. It often does this by using high efficiency and integrating renewable energy.
Nominal Capacity
The rated capacity of an HVAC system under standard conditions, often used for sizing and selection.
Nominal Size
The standard size designation for HVAC components, such as ductwork or piping, which may differ from the actual dimensions.
Non-Ducted System
An HVAC system that does not use ductwork, such as a ductless mini-split or radiant heating system.
Non-Isothermal Flow
The flow of air or fluid with temperature variations, often considered in HVAC system design.
Non-Zoned System
An HVAC system that treats the whole building as one zone. It lacks independent temperature control for different areas.
Normal Load
The typical heating or cooling demand of a building under standard operating conditions.
Noise Reduction Coefficient (NRC)
A measure of a material’s ability to absorb sound, often used in HVAC to reduce noise levels.
NEMA Motor
A motor built to NEMA standards, ensuring compatibility and performance in HVAC applications.
NEMA Starter
A NEMA-standard motor starter ensures reliable operation and protection for HVAC equipment.
Net Zero Carbon
A building or HVAC system with zero net carbon emissions. This is usually done by using energy efficiency and renewable energy sources.
Night Setback
A control strategy that reduces heating or cooling during unoccupied hours, saving energy.
Nitrogen Charge
The process of pressurizing an HVAC system with nitrogen gas to test for leaks or prevent contamination.
Noise Dampening
Techniques or materials used to reduce noise in HVAC systems, such as insulation or vibration isolators.
Non-Condensing Boiler
A boiler that does not recover heat from flue gases, typically less efficient than condensing boilers.
Non-Overloading Motor
A motor designed to handle high starting currents without overheating, often used in HVAC compressors.
Non-Return Damper
A damper that allows airflow in only one direction, preventing backflow in ventilation systems.
NPSH (Net Positive Suction Head)
See Net Positive Suction Head above.
O
ccupancy Sensor
A device that detects the presence of people in a room and adjusts HVAC settings (e.g., temperature or ventilation) to save energy.
Odor Control
Methods to get rid of bad smells in HVAC systems include activated carbon filters and UV lights.
Off-Peak Cooling
A strategy that uses thermal storage or other methods to shift cooling loads to off-peak hours, reducing energy costs.
Oil Furnace
A heating system that uses oil as its fuel source, often found in areas without access to natural gas.
Oil Trap
An oil separator in a refrigeration system removes oil from the refrigerant. This helps keep the system lubricated and running well.
On/Off Control
A basic control method lets an HVAC system run at full power or turn off completely. There are no middle settings.
Open Loop System
A type of geothermal heat pump system that uses groundwater or surface water as the heat exchange medium.
Operating Pressure
The pressure at which an HVAC system is designed to operate, often specified for refrigerant or water systems.
Orifice
A small opening or hole used to control the flow of air, water, or refrigerant in HVAC systems.
Outdoor Air
Fresh air drawn from outside a building and used for ventilation or cooling in an HVAC system.
Outdoor Coil
The condenser coil in an air conditioning or heat pump system, located in the outdoor unit.
Outdoor Unit
The portion of a split HVAC system located outside a building, typically containing the compressor, condenser coil, and fan.
Overload Protector
A safety device that shuts off an HVAC component (e.g., compressor or motor) if it draws too much current or overheats.
Oversizing
Installing an HVAC system with too much capacity can cause problems. It may run inefficiently, cycle on and off too often, and perform poorly.
Ozone
A molecule composed of three oxygen atoms (O₃). While ozone in the upper atmosphere is beneficial, ground-level ozone is a pollutant. Some HVAC systems use ozone generators for air purification, but this is controversial due to health risks.
Ozone Depletion Potential (ODP)
A measure of a substance’s ability to damage the ozone layer. Refrigerants with high ODP, such as CFCs, are being phased out.
Ozone Generator
A device that produces ozone, sometimes used in HVAC systems for air purification. However, its use is limited due to potential health hazards.
Ozone Layer
A layer of ozone in the Earth’s stratosphere that protects against harmful ultraviolet (UV) radiation. HVAC refrigerants can impact the ozone layer if they contain ozone-depleting substances.
Ozonosphere
Another term for the ozone layer, emphasizing its role in protecting the Earth from UV radiation.
Open Circuit Cooling Tower
A type of cooling tower where water is directly exposed to the air, allowing for evaporative cooling.
Operating Temperature
The range of temperatures at which an HVAC system is designed to operate efficiently and safely.
Orifice Plate
A device with a precisely sized hole used to measure or control the flow of air, water, or refrigerant in HVAC systems.
Outdoor Design Temperature
The temperature used as a reference for sizing HVAC systems, based on local climate data and extreme conditions.
Outdoor Reset Control
A control strategy changes the water temperature in a hydronic heating system. It does this based on the outdoor temperature. This change helps improve efficiency.
Overcooling
An HVAC system can sometimes cool a space too much. This causes discomfort and wastes energy.
Overhead Heating
A heating system that spreads warmth from above, often using radiant panels or ducts.
Overpressure
A condition where the pressure in an HVAC system exceeds its design limits, potentially causing damage or failure.
Oxidation
A chemical reaction that occurs when a material is exposed to oxygen, often leading to corrosion in HVAC components.
Oxidizer
A device or substance that promotes oxidation, sometimes used in HVAC systems to remove contaminants from air or water.
Oxygen Scavenger
A chemical removes dissolved oxygen from water in hydronic heating systems. This helps prevent corrosion.
Open System
A type of HVAC system that interacts with the environment, such as a cooling tower or geothermal heat pump.
Operating Cost
The cost of running an HVAC system, including energy, maintenance, and repairs.
Operating Life
The expected lifespan of an HVAC system or component under normal operating conditions.
Optimum Start
A control strategy that calculates the best time to start an HVAC system to reach the desired temperature by a specific time.
Orifice Tube
A fixed metering device used in some refrigeration systems to control the flow of refrigerant.
Outdoor Reset
See Outdoor Reset Control above.
Overcurrent Protection
A safety feature that shuts off an HVAC system if the electrical current exceeds a safe level.
Overhead Duct
Ductwork installed above a ceiling or in an overhead space, often used in commercial buildings.
Overload Relay
A device that protects HVAC motors from overheating by interrupting the electrical circuit if the current is too high.
Ozone-Friendly Refrigerant
A refrigerant with low or zero ozone depletion potential (ODP), such as HFCs or natural refrigerants like CO₂ or ammonia.
P
Packaged Unit – An all-in-one HVAC system that contains heating and cooling components.
Programmable Thermostat – A thermostat that allows users to set heating and cooling schedules.
Plenum – A duct section that distributes or collects conditioned air before it enters supply ducts.
Psychrometrics is the study of air properties. This includes temperature, humidity, and pressure. It is important for HVAC design.
Pressure Drop – The loss of air pressure as it moves through ducts, filters, or coils.
Programmable Thermostat – This thermostat lets you set temperature schedules to save energy.
Pilot Light – A small, continuously burning flame used to ignite the main burner in older gas furnaces.
PTAC (Packaged Terminal Air Conditioner) – This unit heats and cools itself. You often see it in hotels and apartments.
Pump Down – A method of removing refrigerant from the evaporator into the condenser for maintenance or servicing.
Positive Pressure – This happens when indoor air pressure is higher than outdoor air pressure. It helps reduce air infiltration.
Pressure Relief Valve – A safety tool that helps manage excess pressure in HVAC and refrigeration systems.
Purge Cycle – A process that removes unwanted air, moisture, or non-condensables from an HVAC system.
Phase Loss – This happens when one phase fails in a three-phase power supply. It can harm HVAC motors and compressors.
P-trap – This U-shaped pipe stops clogs in the condensate drain line. It also keeps sewer gas from entering the system.
Q
Quadrant Damper – A manually adjustable damper used to regulate airflow in duct systems.
Quenching – This means quickly cooling gases or materials. It’s often used in HVAC and refrigeration.
Quick Connect Fittings – Pre-fabricated refrigerant line connections that allow easy installation without brazing.
Quantity of Airflow (CFM – Cubic Feet per Minute) – A measurement of the volume of air moving through an HVAC system.
Quiet Mode – A feature in some HVAC systems that makes the fan and compressor quieter for a more silent operation.
Quaternary Refrigerants – A blend of four different refrigerants designed for specific HVAC applications.
R
R-22 Refrigerant – A refrigerant that has been phased out and was commonly used in older A/C units.
R-410A Refrigerant – A modern, environmentally friendly refrigerant.
Refrigerant – A chemical compound that absorbs and releases heat to cool air.
Reversing Valve – A key component in heat pumps that switches between heating and cooling modes.
Return Air – Air that is drawn back into the HVAC system from the conditioned space for reprocessing.
Relative Humidity (RH) – The percentage of moisture in the air compared to the maximum it can hold at a given temperature.
Reciprocating Compressor – A type of compressor that uses pistons to compress refrigerant gas.
Radiant Heating – A heating method that transfers heat directly from surfaces (e.g., floors, walls) to people and objects.
Reheat Coil – A coil used to warm air that has been cooled for dehumidification, commonly found in commercial HVAC systems.
Refrigerant Charge – This is the amount of refrigerant in an HVAC system. It needs to be at the right level for the system to work efficiently.
Refrigerant Cycle – This is how refrigerant takes in and gives off heat while moving through the HVAC system.
Relief Damper – A damper that allows excess air to escape to prevent over-pressurization.
Register – This is a vent cover that has adjustable louvers. You can use it to control the direction and volume of airflow.
Return Duct – This duct moves air from the conditioned area back to the HVAC unit for reconditioning.
RTU (Rooftop Unit) – A self-contained HVAC system installed on the roof of commercial buildings.
Refrigerant Leak Detector – This tool finds leaks in HVAC systems that use refrigerant.
Rotary Compressor – This compressor uses rotating blades or vanes to compress refrigerant effectively.
Reheat System – This system warms up cooled air. It helps control humidity and keeps comfort levels steady.
S
SEER (Seasonal Energy Efficiency Ratio) is a way to measure how well an air conditioner or heat pump cools.
Split System – An HVAC system with separate indoor and outdoor units.
Static Pressure – The resistance to airflow in a duct system, measured in inches of water column (in WC).
Supply Air – Conditioned air that is delivered to a space through ductwork or vents.
Superheat – This is the temperature of refrigerant vapor above its boiling point. It helps ensure the system works properly.
Subcooling – The cooling of refrigerant liquid below its condensation temperature to improve efficiency.
Scroll Compressor – This compressor uses a spiral design to compress refrigerant efficiently.
Sensible Heat – The heat energy that causes a change in temperature without changing moisture content.
Saturation Temperature – The temperature at which refrigerant changes phase between liquid and vapor.
Setpoint – The desired temperature set on a thermostat or control system.
Short Cycling – This happens when an HVAC system turns on and off too often. It cuts down on efficiency and shortens the system’s lifespan.
Smart Thermostat – A thermostat that learns user preferences and can be controlled remotely.
Swamp Cooler (Evaporative Cooler) – A system that cools air by using water evaporation.
Solenoid Valve – This valve controls the flow of refrigerant or fluid in HVAC systems using electricity.
Step Capacitor – A capacitor used to regulate voltage and improve motor efficiency.
System Charge – The correct amount of refrigerant required for optimal HVAC system performance.
Supply Duct – A duct that delivers conditioned air to different areas of a building.
T
Thermostat – A device that regulates temperature by controlling the HVAC system.
Ton of Refrigeration – A unit of cooling capacity equal to 12,000 BTUs per hour.
TXV (Thermal Expansion Valve) – This valve controls refrigerant flow to the evaporator. It helps ensure efficient cooling.
Thermal Conductivity – The ability of a material to transfer heat.
Thermal Zone – An area in a building where a thermostat controls the temperature.
Total Heat (Enthalpy) – The sum of sensible and latent heat in an air conditioning system.
Trunk Duct – The main duct that distributes conditioned air to smaller branch ducts.
Two-Stage Compressor – This type of compressor runs at two speeds. It boosts efficiency and enhances comfort.
Thermistor – A temperature-sensitive resistor used in HVAC systems for accurate temperature sensing.
Temperature Differential – This refers to the difference in temperature between the inside and outside, or between the supply and return air.
Time Delay Relay – A control device that delays the startup of a compressor or fan to prevent short cycling.
Tonnage – A measurement of an HVAC system’s cooling capacity.
Thermal Efficiency – The ratio of useful heating or cooling output to energy input.
Turbulence – The irregular airflow in ducts that can reduce HVAC system efficiency.
Total External Static Pressure (TESP) is the airflow resistance in an HVAC system. It impacts how well the fan works.
U
U-Factor (U-Value) – A measure of how well a material (such as a window or insulation) conducts heat; lower values indicate better insulation.
Underfloor Heating – A radiant heating system installed beneath flooring to provide warmth.
Upflow Furnace – A furnace that pulls in air from the bottom, heats it, and then pushes it upward through ductwork.
Unitary HVAC System – This is a self-contained system for heating and cooling. It’s usually found in homes or small businesses.
Ultraviolet (UV) Light Purifier – A system that uses UV light to kill bacteria, mold, and viruses in HVAC systems.
Unconditioned Space – Areas in a building that are not heated or cooled, such as attics or garages.
Undercharge – This happens when an HVAC system has too little refrigerant. It causes the system to work poorly.
Utility Demand Charge – This fee is based on the highest electrical demand during a billing period. It usually impacts commercial HVAC costs.
Upflow Air Handler – An air handler that directs conditioned air upward into ductwork.
Unbalanced Airflow – This happens when supply and return airflow aren’t equal. It causes pressure imbalances.
V
Variable Air Volume (VAV) System – An HVAC system that adjusts airflow based on demand to improve efficiency.
Ventilation – The process of exchanging indoor and outdoor air to improve air quality.
Vacuum Pump – A tool used to remove air and moisture from a refrigeration system before charging it with refrigerant.
Variable Refrigerant Flow (VRF) is a smart HVAC technology. It lets different indoor units work separately, boosting efficiency.
Voltage Drop – This is the decrease in electrical voltage as it moves through wires. It can impact how well the HVAC system runs.
Vent Cap – A cover placed on vents or ducts to prevent debris, rain, and animals from entering.
Velocity Pressure – The pressure exerted by moving air in an HVAC duct system.
Vapor Barrier – This material stops moisture from building up in walls, ceilings, and floors in HVAC systems.
Ventilation Rate – The amount of fresh air supplied to a space, usually measured in CFM (Cubic Feet per Minute).
Vacuum Switch – This is a pressure-sensitive switch in HVAC systems. It checks and controls airflow or gas flow.
Vane Axial Fan – A type of fan designed to move large volumes of air efficiently in HVAC ductwork.
Volatile Organic Compounds (VOCs) are harmful chemicals. They come from building materials and furniture. These compounds can lower indoor air quality.
Ventilation Load: This is the heating or cooling needed to keep air quality and comfort in a building.
X
X-13 Motor – This high-efficiency ECM (electronically commutated motor) is used in HVAC blowers. It helps save energy.
Xylene is a solvent in some HVAC adhesives and sealants. It can impact indoor air quality.
X-Dry Mode – This feature in some air conditioners boosts dehumidification while cooling less.
Y
Y Terminal – This terminal controls the air conditioning compressor or the cooling cycle.
Yaw Angle – This is the angle that airflow deviates in ventilation systems. It impacts how well air is distributed.
York® makes HVAC equipment for homes and businesses. They produce heating and cooling systems that are well-known in the industry.
Y-Strainer – This device filters out debris in HVAC piping. It helps prevent clogging in water and refrigerant lines.
Yield Point – The stress level at which a duct or HVAC material starts to deform permanently.
Yellow Jacket® – A popular brand of HVAC tools and equipment, including refrigerant gauges and vacuum pumps.
Z
Zoning System – This HVAC system splits a building into zones. Each zone can have its own temperature control.
Zone Damper – A damper installed in ductwork to regulate airflow in different zones of a building.
Zone Control – This system uses multiple thermostats and dampers. It helps manage temperature in different areas.
Zero Clearance – An HVAC unit made to fit in tight spaces with little room around it.
Z-Factor: This is a correction factor used in duct design. It accounts for changes in air pressure and velocity.
Zoning Panel – A control board that manages dampers and thermostats in a zoned HVAC system.
Zonal Heating: This system warms specific areas instead of heating the whole building.
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