HVAC Glossary of Terms

This handy glossary of terms informs you of what you need to know about your HVAC system.

13 SEER
Seasonal Energy Efficiency Ratio, an equipment efficiency rating that measures how much energy it takes to cool the air. The new minimum efficiency standard (effective January 2006) is 13 SEER. All new units must now meet this standard

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 AC system so that the right amount of air is delivered to the right places 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, all equipment manuals and show the owner 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.

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.

FAN COIL
See AIR HANDLING UNIT above.

FURNACE
A self-contained heating unit 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 AC systems and heat pumps. HCFCs are thought to contribute to the depletion of the earth’s ozone layer.

HEAT EXCHANGER
The part of a furnace that transfers heat from burning fuel to the air used to heat a building. Also, from a boiler to water for hydronic heating. It can also be a device, such as a condenser or evaporator, in which heat is added or removed in order to heat or cool a space.

HEAT PUMP
A single refrigeration system designed to provide both heating and cooling, as opposed to a separate furnace or air conditioner.

HRV
Heat Recovery Ventilator, a machine that brings fresh air into a home through a process that preheats the air so it requires less energy to heat the space, thus reducing energy costs.

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

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, Ventilation and Air Conditioning.

HVACR
Heating, Ventilating, Air conditioning, and Refrigeration.

INFILTRATION
Air that enters 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.

LOAD CALCULATION
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.

MANUAL D®
An ACCA procedure covering the proper design, installation, maintenance, and repair of ductwork.

MANUAL J®
An ACCA procedure covering the method for calculating heating and cooling requirements (load calculation) for single-family detached homes and mobile homes.

MANUAL RS®
An ACCA publication covering the design, installation, and commissioning of a residential HVAC system.

MATCHED SYSTEM
An air conditioner or heating system comprised of equipment that has been certified by ARI to work together to deliver the specified heating and cooling capacity at the stated efficiency rating.

MOLD
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 “blue” in blue cheese, and are used to make wine, penicillin, and antibiotics. However, some molds can cause health problems.

NATE
North American Technician Excellence, the nonprofit organization that tests and certifies HVACR technicians.

PMA
Planned maintenance agreement, which provides regular maintenance of your HVACR system. Most ACCA member contractors offer PMAs, although they may use different names for them, such as Maintenance Inspection Agreement, Planned Service Agreement, Energy Service Plan, etc.

R-22
(Freon) 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.

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.

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.

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.

SENSIBLE HEAT
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.

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.