Common HVAC Terms

Heating & Cooling Terminology

To search for a specific term, use the index below to navigate to a specific letter.


Accumulator:Storage tank which receives liquid refrigerant from evaporator and prevents it from flowing into the suction line before vaporizing.
AFUE:Annual Fuel Utilization Efficiency.  Indicated as a percentage, your furnace AFUE tells you how much energy is being converted to heat.
Air Handler:The evaporator section of an air conditioning system that circulates and delivers the conditioned air.  The air handler is often referred to as the indoor unit.  It contains the evaporator coil, indoor fan motor and generally a heat strip for supplemental heating.
Air Infiltration:Leakage of air into rooms through cracks, windows, doors and other openings.
BTU:British Thermal Unit.  BTU is a measure of the heat given off when fuel is combusted.  One BTU is equal to the heat given off by a wooden kitchen match.
Capacity:The ability of a heating or cooling system to heat or cool a given amount of space.  For heating, this is usually expressed in BTU.  For cooling, it is usually given in tons.
Charge:The amount of refrigerant placed in a refrigerating unit.
Compressor:Part of a split system heat pump or air conditioner outdoor unit that controls the pressure applied to the refrigerant, necessary for taking in heat to warm your home or getting rid of heat to keep your home cool.
Condenser Coil:Part of a split system air conditioner or heat pump.  By converting refrigerant that is in a gas form back to a liquid, the coil sends heat carried by the refrigerant to the outside.
Condensing Unit:This section of an air conditioning system pumps vaporized refrigerant from the air handler, compresses it, liquefies it and returns it.  It is often referred to as the outdoor unit.
Damper:A type of “valve” used in ductwork that opens or closes to control airflow.  Used in zoning to control the amount of warm or cold air entering certain areas of your home.
Decibel (db):A decibel describes the relative loudness of a sound.  Some common sounds are fairly close to a typical air conditioner or heat pump’s sound level:  human voice, 7.0 decibels;  blender, 8.8.  The average sound rating range from 7.0 to 8.0 decibels.
Defrost Cycle:The process of removing ice or frost buildup from the outdoor coil during the heating season.
Dehumidification:The reduction of water vapor in the air by cooling the air below the dew point; removal of water vapor from the air by chemical means, refrigeration, ect..
Downflow:A type of furnace that takes cool air from the top and blows warm air to the bottom – common when your furnace must be located in a second floor closet or utility area.
Duct:A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.
Ductwork:Pipes or channels that carry air throughout your home.  The delivery system through which warm air from the furnace is brought to where it’s needed.  Ductwork is made of sheet metal, fiberglass, or flexible plastic, and can be round or rectangular in shape.
Efficiency:A rating on comfort equipment is similar to the miles per gallon rating on your car.  The higher the rating number, the more efficient the system and the lower your fuel consumption will be.  You can save a lot of money with a high efficiency unit.
Air Cleaner:
An electronic device that filters out large particles and contaminants in indoor air.  It then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.
Emergency Heat:The back up electric heat built into a heat pump system.  The same as an auxiliary heater, except it is used exclusively as the heat source when the heat pump needs repair.
Evaporator Coil:Part of a split system air conditioner or heat pump located indoors.  The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air.  The warmest refrigerant is then carried through a tube to the outdoor unit (condenser coil).
Fan Coil:An indoor component of a heat pump system, used in place of a furnace, to provide additional heating on cold days when the heat pump does not provide adequate heating.
Filter:Device used for removal of airborne impurities or unwanted elements from liquids. Filtering or “cleaning” the re-circulated air in a residential or commercial building can be done by a variety of products with differing levels of efficiency.  Standard cardboard frame filters are only about 15% effective in removing dust and particles, and have no effect on pollen, micro-organisms, smoke, and similar pollutants.  Electrostatic filters are much more effective.  Electronic air cleaners and HEPA (High Efficiency Particulate Air) filters produce the best results.
Furnace:The part of an environmental system which converts gas, oil, electricity or other fuel into heat for distribution within a structure.
Heat Pump:A heat pump is a reverse cycle air conditioner.  It uses a compression cycle system to supply heat or remove heat from a temperature controlled space.  When you run your air conditioner, your outdoor unit will be blowing hot air (removing heat from your home and sending it outside).  When you run your heat pump, you reverse the flow of refrigerant and remove the heat from the atmoshpere outside and blow it inside.  When the temperature dips below 40 degrees outside, the heat strip switches on to provide supplemental heat.  Heat strips are very expensive to operate.  In southern climates, such as Florida, heat pumps are very efficient.  A 3 to 1 savings in heating compared to electric heat strips.
HFC:Hydrofluorocarbon.  A class of refrigerants.
Horizontal Flow:A type of furnace, installed on its side that draws in air from one side, heats it and sends the warm air out on the other side.  Most often used for installations in attics or crawl spaces.
HSPF:Heating Seasonal Performance Factor.  This is similar to SEER, but it measures the efficiency of the heating portion of a heat pump.  SEER, industry minimums have been raised recently.  The minimum is now 6.80 HSPF.
Humidifier:A piece of equipment that adds water vapor to heated air as it moves out of the furnace.  This adds necessary moisture to protect your furnishings and reduce static electricity.
Humidity:The amount of moisture in the air.  Air conditioners remove moisture for added comfort.
HVAC:Heating, ventilating and air conditioning refers to the indoor comfort industry.
Infiltration:Air flow inward into a space through walls, leaks around doors, windows, or through building materials in the structure.
Load Estimate:A series of studies performed to determine the heating or cooling requirements of your home.  An energy load analysis uses information such as the square footage of your home, window and door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, heat pump or air conditioner.
Matched System:A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when used together, and when used according to design and engineering specifications.
Operating Cost:The day to day cost of running your home comfort equipment, based on energy use.
Package Unit:A self contained air conditioning unit that includes both the evaporator and condenser sections within a single cabinet.  It’s advantages include simplicity of installation, which leads to lower installation costs.  However, a package unit can create more noise and can be less energy efficient than a split system.
Reciprocating Compressor:A type of compressor used in air conditioners that compress refrigerant by using a type of “piston” action.
Reclaiming:Returning used refrigerant to the manufacturer for disposal or reuse.
Recycling:Removing, cleaning and reusing refrigerant.
Refrigerant:Absorbs heat by a change of state (evaporation) from a liquid to a gas, and releases heat by a change of state (condenses) from a gas back to a liquid.  Freon® is the name commonly used for refrigerant, but this is a brand name registered by Dupont.  The correct name for this gas is R-22.  It is chlorofluorocarbon (CFC), and its use is strictly regulated by the Federal Government due to its effect on the ozone layer of the atmosphere.
Register:Combination grille and damper assembly covering an air opening or end of an air duct.
SEER:Seasonal Energy Efficiency Ratio.  This is the approximate efficiency of an air conditioning unit over a season in a given climate.  In the past, a unit with a SEER of 8.00 was considered standard efficiency and a unit with a 10.00 SEER was considered high efficiency.  Since January 1st, 1992, the minimum SEER required by the DOE is 10.00 and 15.00+ SEER is considered high efficiency.
Scroll Compressor:A specially designed compressor that works in a circular motion versus and up and down piston action.
Setback Thermostat:A state of the art electronic thermostat with a built in memory that can be programmed for different temperature settings at different times of the day.
Sound Rating Number (SRN):
Sound is measured in bels (a bel equals 10 decibels).  The SRN of a unit is based on ARI test, performed at ARI standard rating conditions.  Average sound rating range is from 7.0 to 8.0 decibels.  The lower the SRN rating, the quieter the unit.
Split System:Refers to an air conditioner or heat pump that has components in two locations.  Usually one part of the system is located inside (evaporator coil) and the other is located outside you home (condenser coil).
Straight Cool:This is an air conditioner that uses different forms of heating such as natural gas, LP gas, electric resistance heat and oil.
Thermostat:Unit that monitors and controls your HVAC system.
Time Delay:Usually refers to a device that will not allow the condenser to restart for an average of five minutes.
Ton:Heat pumps and air conditioners are generally sized in tons.  Typical sizes for a single family residences are between two and five tons.  Each ton equals 12,000 BTU’s per hour.
Upflow:A type of furnace that draws cool air from the bottom and blows the warmed air out the top into the ductwork.  This type of furnace is usually installed in a basement or an out of the way closet.
Ventilator:A ventilator captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.
Zoning:A way to increase your home comfort and energy efficiency by controlling when and where heating and cooling occurs in a home.  Programmable thermostats are used to control operating times of the equipment.  Dampers are used to direct airflow to certain areas of the home.