HVAC Glossary

A Glossary of HVAC Terms
Confused by the many terms and acronyms surrounding your indoor comfort system? Don’t be! This handy glossary of terms will tell you what you need to know when discussing your HVAC system with a professional contractor.

13 SEER This is the new minimum efficiency standard (effective January 2006) for an air conditioner or heat pump.  All new units must now meet this standard.  Previously manufactured equipment may be used, sold, and installed.  SEER is defined later. ACCA The Air Conditioning Contractors of America, a national trade association that represents heating, ventilation, air conditioning, and refrigeration contractors.

AIR HANDLING UNIT Equipment with a heating element and/or cooling coil and other components in a cabinet or casing.

ARI Air-Conditioning and Refrigeration Institute, a non-profit, voluntary organization composed of heating, air conditioning and refrigeration manufacturers.  ARI publishes standards for testing and rating heat pumps and air conditioners.

BALANCING or AIR BALANCING Adjusting an air conditioning system so that the right amount of air is delivered to the right places in your home in order to achieve the right heating or cooling effect.

BTU British Thermal Unit, the measurement of heating and air conditioning capacity.  A BTU is the amount of heat that must be added to one pound of water to raise its temperature one degree Fahrenheit.

CFC Chlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps, linked to the depletion of the ozone layer.

COP Coefficient of performance, an efficiency ratio that compares the amount of heat delivered to the amount of energy used.  As with MPG on a car, the higher the score the more energy efficient the equipment is.

COIL A heating or cooling element made of pipe or tubing, usually with plates or fins.  COMMISSIONING The final step in installing a heating or air conditioning system.  Every component is checked and tested for compliance with codes, ACCA manuals, manufacturer requirements, and occupant needs. After commissioning, the technician will: provide documentation of testing, provide all equipment manuals, and show the homeowner how to operate the system.

CONDENSER (HEAT EXCHANGER) The outside unit of a heating or air conditioning system. Here the refrigerant condenses from a gas to a liquid and hot or cold air from the building is released to the outside.

DEHUMIDIFIER A device that removes excess moisture from the air.

DOE The U.S. Department of Energy, the federal agency that sets industry efficiency standards.

DUCT Conduits used to carry air. They can be round or rectangular, sheet metal or fiberglass or vinyl tubes. In air conditioning systems they carry air from the home to the air conditioning system or furnace and back to the  home.

ERV Energy Recovery Ventilator, a machine that draws fresh air into the home and exhausts stale air from the home.  It uses a process to preheat or pre-cool (depending on the season) to reduce energy costs associated with
conditioning the air.

ENERGY STAR® A government supported branding used to identify energy efficient products.  The branding was developed by the US Department of Energy and the US Environmental Protection Agency.

EPA The U.S. Environmental Protection Agency.


FURNACE A self-contained heating unit that is designed to deliver heated air to a home.

GAMA Gas Appliance Manufacturing Association is a national trade association serving the interests of manufacturers of gas, oil, and electric appliances and equipment, components and related products used in residential, commercial, and industrial applications.

HCFC Hydrochlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps.  HCFCs were thought to contribute to the depletion of the earth’s ozone layer.

HEAT EXCHANGER 1. The part of a furnace that transfers heat from burning fuel to the air used to heat your home.  Also, from a boiler to water for hydronic heating. 2. A device, such as a condenser or evaporator, in which heat is added or removed in order to heat or cool your home.

HEAT PUMP A single refrigeration system designed to provide both heating and cooling.  Compare to a furnace and an air conditioner, separate units that only heat or cool.

HRV Heat Recovery Venilator, a machine that brings fresh air into a home through a process that preheats the air so it has less impact on your utility bill.

HFC Hydroflorocarbon, used as a refrigerant in air conditioners and heat pumps.  It has little or no effect on the ozone layer.

HSPF Heating Seasonal Performance Factor, an equipment efficiency rating. As with MPG on a car, the higher the rating the more fuel efficient the equipment is.

HUMIDIFIER A device that adds moisture to warm air for your home.

HVAC Heating, ventilating, and air conditioning

HVACR Heating, ventilating, air conditioning, and refrigeration

INFILTRATION Air that enters your home through holes, gaps, and cracks, (e.g., plumbing or electrical holes, the heating and air conditioning system, doors, and windows).

IAQ Indoor air quality

LATENT HEAT The energy that suspends moisture vapor in the air

R-410A The refrigerant that replaces R-22. It does not contain chlorine and is not hazardous to the environment.

REFRIGERANT A fluid that absorbs heat at low temperatures and rejects heat at higher temperatures. 

(or, “charging the refrigerant”)   The procedure an HVACR technician performs to ensure that the system has enough of the right kind refrigerant for peak operating performance. 

The percent of moisture actually in the air compared to the maximum amount of moisture the air can hold at that temperature.

RETURN, RETURN AIR, RETURN SIDE The path the air takes to get to an air-handling unit or furnace so it can be cooled or heated.  It is the “return” path. The return side should be “balanced” with the supply side to ensure
proper air flow and comfort.

SEER Seasonal Energy Efficiency Ratio, an equipment efficiency rating that measures how much energy it takes to cool the air.  As with MPG on a car, the higher the number the more efficient the unit. 

The temperature of the air.  This type of heat is measured with a thermometer.

SPLIT SYSTEM A two-component heating and cooling (heat pump) or cooling only (air conditioner) system.  The condensing unit is installed outside, the air handling unit is installed inside (preferably in conditioned space).Refrigerant lines and wiring connect them together.

SUPPLY or SUPPLY SIDE The part of an HVAC system that takes (supplies) the conditioned air from the air-handling unit or furnace to your home.  The supply side should be “balanced” with the return side to ensure proper air flow and comfort. 

A single HVAC system that can meet different heating and cooling needs in different areas (zones). Each zone of a home has its own thermostat with which it can regulate the temperature and humidity in its area.  One “zoned air conditioner” could be set for a high temperature in one zone and for a lower temperature in the other zone.  Zone systems have two or more zones.

2009 www.acca.org