Glossary of Terms

A
AC Abbreviation for alternating current, a type of electric current in which the polarity is constantly reversing causing the electron flow to reverse.

ACCA Air Conditioning Contractors of America

A-Coil A heat exchanger consisting of two diagonal coils that are joined together in a manner that looks like the letter "A".

AFUE Annual Fuel Utilization Efficiency. A measure of a gas furnace's efficiency in converting fuel to energy - the higher the rating, the more efficient the unit.

AGA Abbreviation for American Gas Association, Inc.

Air Conditioner Any device that can change the temperature, humidity or general quality of the air.

Air cleaner Any device that removes undesirable particles from moving air.

Air flow volume The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper air flow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.

Air handler An air moving and/or mixing unit. Residential air handlers include a blower, a coil, an expansion device, a heater rack and filter. Heaters for air handlers are sold as accessories. In some models heaters are factory installed.

ARI Air Conditioning & Refrigeration Institute

ASHRAE American Society of Heating, Refrigeration and Air Conditioning Engineer

B
BTU British thermal unit; the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit. The heat extracted from your home by an air conditioner is measured in BTUs.

BTUh British thermal units per hour. 12,000 BTUh equals one ton of cooling.

Burner A device that uses fuel to support combustion.

Burner orifice The opening through which gas flows to the air/gas mixing chamber of the burner.

Burner (sealed combustion) A burner that obtains all air for combustion from outside the heated space.

C
Capacity The output or producing ability of cooling or heating systems. Cooling and heating capacities are referred to in British thermal units (BTUs) per hour.

Celsius The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol "C". To convert to Fahrenheit, multiply a Celsius temperature by 9, divide by 5 and add 32 (25 x 9 equals 225, divided by 5 equals 45, plus 32 equals 77 degrees Fahrenheit).

CFM Abbreviation for cubic feet per minute, a standard measurement of airflow. A typical system requires 400 cfm per ton of air conditioning.

Capacity The output or producing ability of a piece of cooling or heating equipment. Cooling and heating capacities are referred to in BTUs.

Charge To add refrigerant to a system. This is refrigerant contained in a sealed system or in the sensing bulb to a thermostatic expansion valve.

Comfort R� Airflow System An exclusive feature of a high efficiency home comfort system from Trane. This method of ramping airflow gives you greater humidity control when cooling and provides warmer air during heating start up.

Compressor This is the heart of an air conditioning or heat pump system. It is part of the outdoor unit and pumps refrigerant in order to meet the cooling requirements of the system.

Condensate Vapor that liquefies due to the lowering of its temperature to the saturation point.

Condenser coil (or outdoor coil) In an air conditioner, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid. In a heat pump system, the coil absorbs heat from the outdoors.

Condenser fan The fan that circulates air over the air-cooled condenser.

Contactor A switch that can repeatedly cycle, making and breaking an electrical circuit. When sufficient current flows through the A-coil built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed.

Crankcase heater This is the electric resistance heater installed on compressor crankcases to boil off liquid refrigerant that may have combined with compressor oil. Many newer cooling systems do not require crankcase heaters, however heat pumps do require crankcase heaters.

CSA Canadian Standards Association.

D
DC Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.

Damper Found in ductwork, this movable plate opens and closes to control airflow. Dampers can be used to balance airflow in a duct system. They are also used in zoning to regulate airflow to certain rooms.

Defrost To melt frost; as in from an air conditioner or heat pump coil.

Degree-day A degree-day is a computation that gauges the amount of heating or cooling needed for a building. A degree-day is equal to 65 degrees Fahrenheit minus the mean outdoor temperature.

Dehumidifier An air cooler that removes moisture from the air.

Diffuser A grille over an air supply duct having vanes to distribute the discharging air in a specific pattern or direction.

DOE Department of Energy

Downflow furnace A furnace that intakes air at its top and discharges air at its bottom.

Drain pan This also referred to as a condensate pan. This is a pan used to catch and collect condensate (in residential systems vapor is liquefied on the indoor coil, collected in the drain pan and removed through a drain line).

Dry bulb temperature Heat intensity, measured by a dry bulb thermometer.

Dry bulb thermometer An instrument that measures air temperature independently of humidity.

Ductwork A pipe or conduit through which air is delivered. Ducts are typically made of metal, fiberboard or a flexible material. In a home comfort system, the size and application of ductwork is critical to performance and is as important as the equipment.

DX Direct expansion; a system in which heat is transferred by the direct expansion of refrigerant.