Glossary of HVAC Terms
AIR HANDLING UNIT (AHU)
Equipment with a heating element and/or cooling coil and other components in a
cabinet or casing.
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.
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.
Chlorofluorocarbons, used as a refrigerant in air conditioners and heat pumps,
linked to the depletion of the ozone layer.
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.
A heating or cooling element made of pipe or tubing, usually with plates or
The final step in installing a heating or air conditioning system. Every
component is checked and tested for compliance with codes, 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.
A device that removes excess moisture from the air.
The U.S. Department of Energy, the federal agency that sets industry
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.
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
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.
The U.S. Environmental Protection Agency.
A self-contained heating unit that is designed to deliver heated air to a
Hydrochlorofluorocarbons, used as a refrigerant in air conditioners and heat
pumps. HCFCs were thought to contribute to the depletion of the earth�s ozone
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.
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
Heat Recovery Ventilator, 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.
Hydroflorocarbon, used as a refrigerant in air conditioners and heat pumps. It
has little or no effect on the ozone layer.
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.
A device that adds moisture to warm air for your home.
Heating, ventilating, and air conditioning
Heating, ventilating, air conditioning, and refrigeration
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).
Indoor air quality
The energy that suspends moisture vapor in the air.
A mathematical determination of how much cooling and heating (BTUs) an HVAC
system must deliver for occupant safety and comfort. It is based on a variety
of factors: square footage, building orientation, number of occupants, size and
placement of rooms, number and size of windows and doors, amount of insulation,
number of floors, and climate.
A natural byproduct of the fungi family that thrives when organic substances
and water combine under certain circumstances. Mold reproduces via spores that
can remain dormant, yet viable, for years. Many molds are beneficial. For
example, they are the �bleu� in bleu cheese, and we use them to make wine,
penicillin, and antibiotics. However, some molds can cause health problems.
A refrigerant containing chlorine used in air conditioning systems. The EPA has
mandated that R-22 cannot be manufactured after 2010 because it has been linked
to the depletion of the ozone layer and global warming. Most commonly referred
to by its trademarked name, Freon.
The refrigerant that replaces R-22. It does not contain chlorine and is not
hazardous to the environment.
A fluid that absorbs heat at low temperatures and rejects heat at higher
REFRIGERANT CHARGE (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.
RELATIVE HUMIDITY (RH)
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.
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.
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
The temperature of the air. This type of heat is measured with a
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.
VARIABLE FREQUENCY DRIVE (VFD)
Automated speed control for electric motors like fans, pumps and centrifugal
chillers for precise control and energy savings
ZONES, ZONED SYSTEM, ZONING
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.