A Portion of All AGL Proceeds Support Charitable Causes


Air Change

Unlike re-circulated air, this is the total air required to completely replace the air in a room or building.

Annual Fuel Utilization Efficiency (AFUE)

A rating that measures the amount of heat your equipment delivers for every dollar spent on fuel. A higher rating indicates more efficient equipment.

Air Conditioner

Equipment that simultaneously controls air temperature, relative humidity, purity and motion.

Air Diffuser

An air distribution outlet or grille that directs airflow into desired patterns.

Air Handler

The part of the central air conditioning or heat pump system that circulates heated or cooled air throughout ductwork. Some furnaces perform this function.


Balance Point

An outdoor temperature, usually between 30° and 45° Fahrenheit, at which a heat pump’s output equals the exact heating needs of the home or business. Below the balance point, supplementary electric resistance heat must maintain indoor comfort.


An air-handling device for moving air in a distribution system.

BTU (British Thermal Unit)

The standard of measurement used for the amount of heat required to raise the temperature of one pound of water by one degree (Fahrenheit). BTUH = the number of BTUs per hour.


Cooling Load

Heat that flows into a space from outdoors and/or indoors.

Cooling Capacity

The measure of a unit’s ability to remove heat from an enclosed space. The COP, or Coefficient of Performance, of a heat pump measures the ratio of the rate of useful heat output that the pump delivers (excluding supplementary heating) to the corresponding rate of energy input.

Condensing Unit

Part of a refrigerating mechanism that pumps in vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it.

Condenser Coil

A series or network of refrigerant tubes typically placed outside a home or business that removes heat from the hot, gaseous refrigerant and re-liquefies it.


Known as “the heart of the system” because it circulates the refrigerant through the loop, the compressor moves the refrigerant from the indoor evaporator to the outdoor condenser, then back to the evaporator.


The ability of a heating or cooling system to function in a given amount of space. Heating = BTUs. Cooling = tons.

Central Air Conditioner System

A system that treats air at a central location and carries it to and from rooms by one or more fans and a system of ducts.

Closed-loop Heat-pump System

A heat-pump system that uses a loop of buried plastic pipe as a heat exchanger. Loops can be horizontal or vertical.



Building-wide air delivery conducted through pipes or channels.

Ductless System

A heating and air conditioning system that usually has a wall-mounted indoor unit and an outside compressor. It does not require ductwork.


Used for conducting air to and from an air-handling unit via a pipe or closed conduit made of materials such as sheet metal or fiberglass board.

Downflow Furnace

Draws in return air from the top and expels warm air at the bottom.


A device for recovering superheat from the compressor discharge gas of a heat pump or central air conditioner for use in heating or preheating water.


The reduction of water vapor by cooling the air below the dew point, as well as the removal of water vapor from air by chemical means, refrigeration, etc.

Defrost Cycle

The removal of ice or frost buildup from the outdoor coil during the heating season.


Found in ductwork, this movable plate opens and closes to control airflow and is used in zoning to regulate airflow to certain rooms.


Evaporative Cooling

Method of cooling that uses water evaporation to cool warm air.

Evaporator Coil

Located inside the home or business, a series or network of tubes filled with refrigerant that removes heat and moisture from indoor air as liquid refrigerant evaporates.


Absorbs heat or liquid from the surrounding air and moves it outside the refrigerated area by means of a refrigerant. Also known as a cooling coil, blower coil, chilling unit or indoor coil.

Energy Efficiency Ratio (EER)

The ratio of an air conditioning unit’s cooling capacity in BTUs per hour to the total electrical energy consumed in watts.

Emergency Heat (Supplemental or Auxiliary Heat)

The backup heat built into a heat pump system.

Electronic Air Cleaner

Type of air purifier that uses electrically charged filters to minimize airborne contaminants.


A fuel-efficiency rating similar to the miles-per-gallon rating on your car.



The part of the system that converts gas, oil, electricity or another fuel into heat for distribution within a structure.


R22 refrigerant, also known as Freon, has been the HVAC industry standard refrigerant used in the manufacture of central air conditioning systems. Because R22 refrigerant contributes to depleting the ozone layer, the U.S. government has enacted a policy requiring that air conditioners and heat pumps no longer use R22 refrigerant. If your existing AC system has R22 refrigerant, it can be serviced and, if necessary, recharged up to January 1, 2020. However, after January 1, 2020, refrigerant manufacturers must cease all production of R22 refrigerant completely. If you are purchasing a new air conditioning system today, consider one that uses the more environmentally friendly R410A refrigerant.


A device that removes dust and other air particles to comfort the respiratory system and protect the heating and cooling equipment. The higher the MERV rating, the better the filter.


Geothermal Heat Pump

A heat pump that uses the earth as a heat source in the winter or a heat sink in the summer. Geothermal systems use a series of water loops that move heat to and from the ground.



The amount of moisture in the air. Air conditioners remove moisture for added comfort.


Regulates humidity input by reacting to moisture content changes in the air.


The process of adding moisture to the air within a space.


Heating, Ventilation and Air Conditioning.

Horizontal Furnace

A sideways furnace that draws in return air from one side and expels warm air from the other.

Heating Capacity

The rate at which a specific device can add substantial heat to a substance, expressed in BTUH (British Thermal Units per hour).

Heating Seasonal Performance Factor (HSPF)

The total heating output of a heat pump in BTUs during its normal usage period for heating, as divided by the total electrical energy input in watt-hours during the same period.

Heat Transfer

The movement of heat from one place to another, between two substances or within a substance.



Airflow into a space usually through walls and leaks around doors and windows. Insulation: Any material that reduces the speed of heat transfer.

Indoor Coil

A refrigerant containing a portion of a fan coil unit similar to a car radiator, typically made of several rows of copper tubing with aluminum fins.

Indoor Unit

Usually located inside the house, it houses the indoor coil, fan, motor and filtering device, sometimes called the air handler.


Kilowatt (kW)

Equal to 1,000 watts of electricity, a kilowatt-hour (kWh) is a common unit of electrical consumption measured by the total energy that one kilowatt creates in an hour.


Load Calculation

Determines a building’s heat gain and loss to ensure installation of properly sized air conditioning and heating equipment.

Latent Cooling Capacity

An air conditioning system’s capability to remove moisture from the air. Latent Heat: The heat energy needed to change the state of a substance (e.g., from a liquid to a gas), but not its temperature.


Matched System

A heating and cooling system consisting of products certified to perform at promised comfort and efficiency levels when used together, in accordance with design and engineering specifications.


Natural-Draft Furnace

A furnace with natural airflow around it that supports combustion. It depends on the pressure that heat creates in the flue gases to force them out through the vent system.


Outdoor Coil/Condensing Unit

The portion of a heat pump or central air conditioning system located outside the home. It functions as a heat transfer point for collecting heat from and dispelling heat to the outside air.

Open-loop Heat-pump System

A heat-pump system that uses groundwater from a well or surface water from a lake, pond or river as a heat source. The water is returned to the environment.

Operating Cost

The day-to-day cost of running your home comfort equipment, based on daily energy use.


Payback Analysis

A general measure of your home comfort system’s efficiency and value. By combining your purchase price with ongoing operating costs, it determines the number of years required before monthly energy savings offset the purchase price.


Reversing Valve

A device in a heat pump that reverses the flow of refrigerant as the system switches from cooling to heating.

Return Air

Air drawn into a heating unit after having been circulated from the heater’s output supply to a room.

Residential Wine Coolers

Wine cellars that are cooled separately from the rest of the home.

Relative Humidity

The ratio of the amount of vapor contained in the air to the maximum amount the air could hold at that temperature, usually expressed as a percentage.


Combination grille and damper assembly covering an air opening or end of an air duct.

Refrigerant Lines

Set of two copper lines connecting the outdoor unit and the indoor unit.


A substance that produces a refrigerating effect while expanding or vaporizing.

Radiant Floor Heating

Type of heating that can be combined with geothermal systems to warm a home’s floors.


Supplementary Heat

Auxiliary or emergency heat, usually electrical resistance heat, provided at temperatures below a heat pump’s balance point.

Split System

The most common type of home central air conditioner, it consists of a compressor (the unit and condenser, installed outside the building) and a non-compressor (the air-handling unit installed within the building).

Single Package

A year-round heating and air conditioning system with all components encased in one unit outside the home.


The temperature at which a thermostat is set for desired comfort level.

Sensible Heat

Heat energy that raises or lowers the temperature of a gas, liquid or solid when added or removed from that material.

Sensible Cooling Capacity

An air conditioning system’s capability to reduce the temperature by removing heat from the air.

Seasonal Energy Efficiency Ratio (SEER)

A rating that denotes the efficiency of air conditioning equipment in terms of the amount of cooling your equipment delivers for every dollar spent on electricity. The higher the SEER, the more efficient the unit and the lower the operating cost.



A brand of air conditioning systems used by AGL Services.


The unit of measure used in air conditioning to describe the cooling capacity of a system. One ton of cooling is based on the amount of heat needed to melt one ton (2,000 lbs.) of ice in a 24-hour period, and equals 12,000 BTUH.


A temperature control device, typically found on an inside wall, that consists of a series of sensors and relays for monitoring and controlling a heating and cooling system.


UV Lights

A type of light that can be used to kill mold on the evaporator coil of a cooling system.

Upflow Furnace

A furnace that pulls return air in from the bottom and expels warm air from the top.


A type of air conditioning system that discharges air into the conditioned space via a top- mounted discharge plenum or through an overhead duct system.



The process of supplying or removing air, by natural or mechanical means, to or from any space. Such air may or may not have been conditioned.

Vapor Seal

A barrier essential to prevent moisture from infiltrating into, or migrating from, a data processing center or other “critical space” that contains sensitive electronic instrumentation. Vapor barriers may be created using plastic film, vapor-retardant paint, vinyl wall coverings and vinyl floor systems, in combination with careful sealing of all openings (doors and windows) into the room.

Vapor Barrier

A moisture-resistant layer applied to the surfaces of humid spaces that prevents moisture from traveling to a point where it might condense due to lower temperature.



A unit of power that equals one joule per second. Named after the Scottish inventor and mechanical engineer James Watt.


A brand of geothermal and water source heat pumps used by AGL Services.



The practice of providing independent heating and/or cooling to different areas within a structure.

Zone System

A method of dividing a home into zones that makes it possible to control the amount of comfort provided to each.