HVAC Terminology

HVAC systems are integral to maintaining comfort in homes and buildings, yet the terminology used can often be complex and confusing. This comprehensive glossary will demystify HVAC terms tp provide clear definitions that homeowners, students, and professionals can easily understand and refer to.

Absolute Humidity: The total mass of water vapor present in a given volume of air.

AC (Air Conditioning): The process of removing heat and moisture from the interior of an occupied space.

Accumulator: A reservoir that stores excess refrigerant vapor to prevent it from entering the compressor.

AFUE (Annual Fuel Utilization Efficiency): A measure of a furnace’s heating efficiency.

Air Balance: Adjusting an HVAC system to ensure that air distribution is evenly spread throughout the space.

Air Changes Per Hour (ACH): The number of times air is replaced in a space per hour.

Air Cleaner: A device that removes contaminants from the air.

Air Handler: The indoor part of the air conditioning or heating system that moves air through ducts.

Airside Economizer: Takes advantage of cool outside air to reduce the need for mechanically cooled air.

Ambient Temperature: The temperature of the air surrounding a given environment.

ARI (Air Conditioning and Refrigeration Institute): An industry group that sets standards for HVAC equipment.

ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers): An international technical society developing standards for HVAC systems.

Backdrafting: The reverse flow of exhaust gases into the indoor space.

Blower: The component in an HVAC system that drives air through the ductwork.

BTU (British Thermal Unit): A unit of heat; the amount needed to raise the temperature of one pound of water by one degree Fahrenheit.

Bypass Damper: A damper used to control or change airflow.

CAV (Constant Air Volume): An HVAC system that provides a constant airflow at a variable temperature.

CFM (Cubic Feet per Minute): A measurement of airflow volume.

Charge: The amount of refrigerant in a system.

Charging Hose: A hose used to add refrigerant to an HVAC system.

Chiller: A machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle.

Coil: Equipment that performs heat transfer to air when mounted inside an air handling unit or ductwork.

Compressor: A pump used to increase the pressure of the refrigerant.

Condensate: Liquid that condenses from a gas during the cooling process.

Condenser: A heat exchanger in which hot vapor is cooled and condenses into a liquid.

Condenser Coil: The outdoor component of an air conditioner or heat pump that expels heat from the refrigerant.

Damper: A plate or valve that controls airflow in ductwork.

Dehumidifier: A device that removes moisture from the air.

Desuperheater: A device that recovers waste heat from the hot gases of a compressor to heat water.

Diffuser: A device that evenly distributes air from an HVAC system.

Ducts: Conduits used in heating, ventilation, and air conditioning to deliver and remove air.

Ductwork: The system of ducts used to transport air from an HVAC unit throughout a building.

EER (Energy Efficiency Ratio): A measure of how efficiently a cooling system will operate when the outdoor temperature is at a specific level (usually 95°F).

Economizer Cycle: A system that uses outside air to reduce the need for mechanically cooled air.

Energy Recovery Ventilator (ERV): A system that exchanges stale indoor air with fresh outdoor air, recovering heat and moisture from the exchanged air.

Evaporator: A component in an HVAC system where liquid refrigerant absorbs heat and evaporates, cooling the air.

Evaporative Cooler: A device that cools air through the evaporation of water.

Expansion Valve: A device in an air conditioning system that controls the amount of refrigerant flow into the evaporator.

Fan Coil Unit (FCU): A simple device consisting of a heating or cooling coil and fan.

Filter: A device used to remove dust and other particles from the air.

Flue: A duct, pipe, or chimney for exhausting combustion gases from a fireplace, furnace, water heater, or boiler to the outdoors.

Furnace: An appliance fired by gas, oil, electricity, or wood in which air or water is heated to be circulated throughout a building in a heating system.

Gauge Pressure: Pressure measured relative to ambient atmospheric pressure.

Grille: A cover with openings through which air is drawn into or out of a duct system.

Heat Exchanger: A system that transfers heat from one medium to another.

Heat Gain: The process of increasing the amount of heat in an area, often due to external factors.

Heat Loss: The transfer of heat from inside a building to the outside, which affects heating loads.

Heat Pump: A device that transfers heat from a cooler area to a warmer area by using mechanical energy, often used for both heating and cooling.

Humidistat: A device used to measure and control the humidity in a space.

Humidifier: A device that adds moisture to the air.

HVAC (Heating, Ventilation, and Air Conditioning): The technology of indoor environmental comfort.

HVACR (Heating, Ventilation, Air Conditioning, and Refrigeration): Represents the broader industry encompassing all aspects of indoor environmental control.

IAQ (Indoor Air Quality): A measure of the cleanliness of air in an indoor environment.

Inverter: A technology that regulates the speed of an electromotor, such as those found in compressors, to vary the heating/cooling output.

Kilowatt (kW): A unit of power equal to one thousand watts.

Load Calculation: The process of determining the proper size of an HVAC system by calculating the building’s heating and cooling needs.

Louvers: Adjustable slats that control air direction and flow in a grille or vent.

Make-Up Air Unit (MAU): A device that brings fresh air into a building to replace exhausted air.

Manifold Gauge: A tool used to measure the pressure of refrigerant in an HVAC system.

Manual J: A standard procedure for calculating residential cooling and heating loads.

Microclimate: The climate of a very small or restricted area, especially when this differs from the area around it.

Modulating Valve: A valve that can be opened or closed incrementally to control the flow of air or fluid.

MUA (Make-Up Air): Air that is brought into a space to replace exhausted air.

NEBB (National Environmental Balancing Bureau): An organization that certifies professionals who test, adjust, and balance HVAC systems.

Plenum: A space or chamber from which air is distributed to various ducts or locations in an HVAC system.

Programmable Thermostat: A thermostat that allows users to set temperatures for different times and days automatically.

PSI (Pounds per Square Inch): A unit of pressure.

Purge Unit: A component used in chiller systems to remove non-condensable gases.

Radiant Flooring: A heating system that provides heat directly to the floor of a building.

Recovery Rate: The rate at which a water heater can raise the temperature of the incoming water.

Refrigerant Charge: The amount of refrigerant in a system.

Register: An adjustable air distribution outlet, typically found on walls or floors.

Relative Humidity: The amount of moisture in the air compared to what the air can hold at that temperature.

Return Air: Air that is returned to a heating or cooling system for reconditioning.

Reversing Valve: A device in a heat pump that reverses the flow of refrigerant to switch between heating and cooling.

SEER (Seasonal Energy Efficiency Ratio): A measure of the cooling efficiency of an air conditioner or heat pump.

Set Point: The temperature to which a thermostat is set to maintain.

Split System: An HVAC system where the condenser and compressor are located outside the building, and the evaporator is inside.

Static Pressure: The resistance to airflow in a heating, cooling, or ventilation system.

Supply Air: Air that is heated or cooled by the HVAC system and supplied to the rooms of the house.

Thermistor: A type of resistor whose resistance varies significantly with temperature.

Thermocouple: A device consisting of two different conductors that produce a voltage related to a temperature difference.

Ton of Refrigeration: A unit of power used in some countries to describe the heat-extraction capacity of air conditioning and refrigeration equipment.

Two-Stage Furnace: A furnace with two levels of heat output: high for cold winter days and low for milder days.

UV Air Purifier: A device that uses ultraviolet light to kill or neutralize microorganisms in the air.

Vacuum Pump: A device that removes gas molecules from a sealed volume to leave behind a partial vacuum.

Variable Frequency Drive (VFD): A type of motor controller that drives an electric motor by varying the frequency and voltage of its power supply.

Variable Refrigerant Flow (VRF): A system of air-conditioning that allows individual control of the air-conditioning in each room or area of a building.

Vent: An opening allowing air to pass out of or into a confined space.

Ventilation: The process of supplying and removing air by natural or mechanical means to or from any space.

VFD (Variable Frequency Drive): Controls the speed of the motor and can significantly increase energy efficiency.

Volatile Organic Compounds (VOCs): Organic chemicals that have a high vapor pressure at ordinary room temperature.

Volume Damper: A type of damper used in ductwork that regulates airflow volume but not the flow direction.

Watt: The basic unit of electric, mechanical, or thermal power in the International System of Units (SI), equal to one joule per second.

Weatherization: Modifications made to a building that help protect it from the elements and increase energy efficiency.

Wet Bulb Temperature: A measure of air temperature that reflects the cooling effect of moisture.

Zoning: The practice of dividing a home into different zones for heating and cooling purposes.

Zone Damper: A device used in zoning to regulate airflow to different rooms or zones.

Zone System: An HVAC system capable of maintaining different temperatures in different areas of a building.

Zoned HVAC: Refers to a system that uses dampers in the ductwork to direct air to certain parts of the home.