Text Size

HVAC Glossary

We know that HVAC terms can be a little confusing. We have put together some of the more common HVAC (Heating, Ventilation, and Air Conditioning) terms and definitions in an easy-to-understand format.


AFUE-Annualized Fuel Utilization Efficiency

A measure of your furnace's heating efficiency. The higher the AFUE percentage, the more efficient the furnace. The minimum percentage established by the DOE for furnaces is 78%. (An easy way to reflect the AFUE value is to think of 100% AFUE as one dollar. An 80% AFUE means 80 cents of the dollar is going into heating the home, the other 20 cents is going out the exhaust).


AHRI-Air Conditioning Heating Refrigeration Institute

AHRI is an industry trade association that develops standards for measuring and certifying product performance. For instance, AHRI Standard 270 provides guidelines for establishing sound levels for outdoor air-conditioning equipment.


Air Conditioner

A method of conditioning the indoor temperature and/or humidity level. Generally this accomplished with 1 or more pieces of mechanical equipment. A window air conditioner is an example of a stand alone system, whereas a central air conditioning system is generally made up of a blower (in the furnace), refrigeration coil, refrigeration lines, and condenser (air conditioner).



The distribution or movement of air.


Air Handler/Coil Blower

The part which has the blower in it. An air handler is usually considered the furnace.



Microscopic living organisms suspended in the air that grow and multiply in warm, humid places.


BTU-British Thermal Unit

A British thermal unit is a unit of heat energy. One Btu is the amount of heat required to raise one pound of water by one degree Fahrenheit. The higher the Btu rating, the greater the heating capacity of the system. 



British thermal units per hour.


CAE-Combined Annual Efficiency

A measure of the amount of heat produced for every dollar of fuel consumed for both home and water heating.


Carbon Monoxide

An odorless, colorless, tasteless, poisonous and flammable gas that is produced when carbon burns with insufficient air.


Central Air Conditioning System

System in which air is cooled at a central location, and distributed to and from rooms by one or more fans and a series of ducts.


CFM-Cubic Feet per Minute

This measurement indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being moved through the ductwork by the system. 


Coil Blower

Mechanical equipment composed of a blower and a refrigeration coil. Two other terms are associated with this: air-handler and an electric furnace.



The part of the outdoor air conditioner or heat pump that compresses and pumps refrigerant to meet household cooling requirements.


Concentric Kit

A combining of 2 pipes into 1. This is generally done for aesthetic value in a 90% furnace application so that only 1 pipe is visible from the roof or side of home.


Condenser Coil

A piece of equipment which air moves through to dispense heat into the air. It looks like a car radiator.


Cross-Over Ducting

Often used phrase for the ducting that connects 2 or more 'halves' of a manufactured home. Sometimes used to refer to ducting going from one room to an adjoining hall or room (to provide air flow without sound or light transfer).



A movable plate, located in the ductwork that regulates airflow. Dampers are used to direct air to the areas that need it most. Typically used in a zoning application. Some register boots have an internal damper built in.


Decibel (dB)

A decibel is a unit used to measure the relative intensity of sound.


DOE-Department of Energy

The Department of Energy is a federal agency responsible for setting industry efficiency standards and monitoring the consumption of energy sources.



Term given to the direction of air-flow. Typically, furnaces installed in down-flow configuration are used in garage or closet installations.


Dual Fuel

A comfort system that pairs an electric heat pump with a natural gas, propane, or oil furnace, providing an energy-efficient alternative to the conventional furnace/air conditioner combination.



The method by which air is channeled from the furnace or the blower coil to specific areas of the home.


EAC-Electronic Air Cleaner

An electronic device that filters out particulates in the indoor air stream. NOTE: Some EAC units can emit ozone.


EER-Energy Efficiency Ratio

The efficiency rating of equipment at a given set of values. Like saying the miles per gallon a car is getting on level ground doing 60 miles an hour, vs. going downhill. The higher the EER, the more efficient that particular system is.



An EPA (Environmental Protection Agency) designation attached to HVAC products that meet or exceed EPA guidelines for high-efficiency performance above the standard government minimums.


EPA-Environmental Protection Agency

The Environmental Protection Agency develops and enforces federal environmental regulations. The EPA oversees the nationwide ENERGY STAR® program.


Evaporator Coil

A piece of equipment through which air moves to extract heat from the air. It looks like a car radiator.


FAQs-Frequently Asked Questions


Filter Grill

A return air grill that accommodates a furnace filter. Generally, these filters are no thicker than 1" to 2".


Fossil Fuel

Natural fuel resource that includes natural gas, oil, and coal. Unlike other resources (i.e. methane, solar, geothermal), these are non-renewable.



Any mechanical device utilized to heat a structure or area. These devices generally include a fan blower, heat exchanger, and electronic controls.


Garage Heater

Garage heaters are furnaces placed specifically to combat cold garages and workshops during the winter months. These units generally hang from the ceiling.


Gas Pack

Term given for a single piece of equipment that heats a particular structure. These units mount on a roof curb or can sit on a concrete slab. From either of these positions, they are ducted into the structure.



Term related to utilization of ground temperature for heating purposes. The transfer heating medium is generally water or a glycol fluid ran through various piping.


Heat Exchanger (furnace)

Located inside the furnace, the heat exchanger transfers radiated heat from fuel combustion to the air stream, which is then pumped throughout the home. The products of combustion are then evacuated out of the heat exchanger and exit the home through flue piping.


Heat Exchanger (ground loop)

The devise in the ground, usually tubing, through which fluid flows for a geothermal system. This fluid extracts heat from the ground in the winter and rejects heat to the ground in the summer.


Heat Pump

A heat pump is an HVAC unit that heats or cools by moving heat. During the winter, a heat pump draws heat into the home from the air (an air to air heat pump), or the ground (a geothermal heat pump). In the summer, it reverses the process and removes heat from your house and releases it to the environment from which it takes heat in the winter.


Horizontal Flow

Term given for the direction of air flow. Typically, furnaces installed in a horizontal application are used in attic or crawl space installations.


HRV-heat recovery ventilator

A system that exchanges contaminated indoor air with fresh air while recovering energy (often about 70% efficient).


HSPF-Heating Seasonal Performance Factor

The Heating Seasonal Performance Factor is the heating efficiency rating for heat pumps in the winter. The higher the rating, the more efficient the heat pump is.



An indoor air quality device that introduces moisture to the space.



An automatic device used to maintain humidity levels.


HVAC-Heating, Ventilation, and Air Conditioning


Indoor Coil

Term given for the refrigeration coil when utilized in a split AC or HP system.


ISO 9000

A family of international standards for quality management and assurance.



Term given for 1000 watt.


Line Set

Term given for the liquid and suction lines that freon must travel between the refrigeration coil and condenser.


LP-Liquid Propane

A by-product fuel (from oil or natural gas) most often used for heating when natural gas is unavailable.


MERV-Minimum Efficiency Reporting Value

A rating system that describes a filter's efficiency---depending on the size of the particles being filtered out. Due to the testing process, it is important to understand both the testing category and the particulate size to accurately understand the true MERV rating of the filter. Basically, the higher the MERV rating is the better efficiency the filter has. Ratings vary from 1 (poor) to 16 (best).



A unit of measure equal to one millionth of a meter, or one thousandth of a millimeter.


NATE-North American Technician Excellence

The standard which tests the training and ability of a service person.



Air contaminants in the form of gases.


Outdoor Coil-See Condenser Coil.



Any substance measuring less than 100 microns in diameter. The EPA has found that small particles (less than 2.5 microns) are responsible for the health effects of greatest concern.


Programmable Thermostat

A thermostat with the ability to operate different temperature/time settings for your heating and/or cooling equipment.



Term given for the supports placed under an air-conditioner or heat pump to elevate it above ground level.


R410A Refrigerant

A chlorine-free refrigerant that meets the EPA's newest, most stringent environmental guidelines.



A chemical that produces a cooling effect while expanding or vaporizing. Most residential air conditioning units contain R-22 refrigerant or the newer R410A refrigerant, often referred to as Freon.


Refrigerant Lines

Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.


RTU-Roof-Top Unit

A term given for the HVAC equipment set on a roof. Generally, this type of equipment is utilized in a commercial building setting.



Term given for insulative values. The higher the R-value, the better the insulation value is on that product.


Scroll Compressor

A specially designed compressor that works in a circular motion, as opposed to up-and-down piston action.


SEER-Seasonal Energy Efficiency Ratio

An energy efficiency rating for air conditioners and heat pumps in summer. The higher the SEER rating, the better the efficiency.


SHGC-solar heat gain co-efficiency

A windows ability to block radiant heat. The lower the number, the better the window's ability to block radiant heat.


Single Package

A heating and cooling system contained in one outdoor unit.


Split System

An HVAC system in which some components are located inside the structure of the house and some are located outside. Split systems should be matched for optimal efficiency.



Monitors temperature and humidity and adjusts heating or cooling system to maintain desired levels.



A device that operates as a control to regulate your heating and cooling equipment, allowing you to adjust your home comfort at the touch of a switch. Generally, thermostats are found on interior walls. Thermostats can be bi-metal, mercury, or digital in function.  



Unit of measurement for determining cooling capacity. One ton equals 12,000 Btuh.


Two-Stage Operation

Provides two levels of heating or cooling output for greater temperature control, energy efficiency, and improved comfort.


TXV-Thermal Expansion Valve

A device that allows specific freon flow through to the indoor coil.


Up flow

Term given to the direction of air flow. Typically, furnaces installed in an up flow configuration are used in basement, closet, and some attic installations.



Term given to describe the window's ability to resist heat transfer through conduction. The lower the value, the better the window can prevent heat transfer through conduction.


Variable Speed Motor

A motor that automatically adjusts the flow of air to maintain efficiency and comfort.


VOC-Volatile Organic Compounds

Term usually associated with off-gassing of paint or other substances. These are solids that want to be in a gas state.


WTA- Water-To-Air

Term given for the transfer of heat from a water source (water heater, geothermal, etc) to air.



A method of partitioning a home into independently controlled comfort zones for enhanced comfort and efficiency.