AFUE - Annual Fuel Utilization Efficiency - Indicated as a percentage, AFUE reflects the efficiency of a gas furnace in converting fuel to energy (heat). The higher the AFUE rating, the more efficient the unit. For example, an AFUE of 90 means that 90% of the fuel is being used to warm your home, while the remaining 10% escapes as exhaust.

ARI - Air Conditioning and Refrigeration Institute – a voluntary, nonprofit organization created by manufacturers of air conditioning, refrigeration, and heating products to ensure an acceptable level of quality within the industry. ARI develops standards for and certifies the performance of cooling and heating products.

BTU - British Thermal Unit - In scientific terms, it represents the amount of energy required to raise one pound of water one degree Fahrenheit. One BTU is equal to the heat given off by a wooden kitchen match. BTU is used for both heating and cooling: it is the measure of heat given off when fuel is combusted for heating or the measure of heat extracted from your home for cooling.

BTUH - British Thermal Units per Hour – the units in which we measure the heat transfer rate of HVAC equipment.

Capacity - Usually measured in BTUs for heating or tons for cooling, capacity refers to the ability of a heating or air conditioning unit to heat or cool a space. A 20-ton air conditioning unit has twice the capacity of a 10-ton unit.

CFM – cubic feet per minute - the units in which we measure air flow. A higher number means more air is being forced through the system.

Carbon Monoxide - a colorless, odorless, poisonous gas, produced by incomplete combustion of carbon-based fuels.

Compressor – Key to keeping your home cool, the compressor controls the pressure applied to refrigerant in order to maintain sufficient flow necessary to eliminate heat from inside your home.

Condenser Coil - Part of the outdoor portion 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.

Decibel (dB) - a unit used to express the intensity of a soundwave. For example, quiet conversation is around 40 dB.

Damper – a device found in ductwork that opens and closes to control airflow. Dampers are used in zoning to regulate airflow to certain rooms.

DOE – Department of Energy - a federal agency that sets the standards for efficiency throughout the HVAC industry and monitors consumption of energy sources.

Downflow - describes the direction of airflow through a furnace. A downflow furnace takes cool air from the top, heats it, and delivers the warmed air out the bottom.

Ductwork - flexible, large-diameter pipes or channels that carry air throughout your home.

Evaporator – The evaporator coil is filled with liquid refrigerant. When warm air passes over the coil, the refrigerant converts to gas and absorbs heat from the air. This gas refrigerant is then pumped through a tube to the outdoor unit where heat is released into the surrounding air and the refrigerant returns to liquid.

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.

Heat Exchanger – part of a furnace that transfers heat from the burner to the blower.

Heat Pump - extracts heat from the outside air and pumps it indoors when in a heating mode and absorbs heat from indoors and forces it outside when in a cooling mode.

Horizontal Flow - describes the direction of airflow through a furnace. A horizontal furnace takes cool air from one side, heats it, and delivers the warmed air out the other side.

HSPF - Heating Seasonal Performance Factor - a measure of the efficiency of a heat pump to heat your home. It is the average number of BTUs of heat delivered by a heat pump for every watt-hour of electricity used over an entire heating season. The higher the number, the more efficient the unit.

Humidifier - a device that adds water vapor to heated air as it moves out of the furnace.

HVAC - Heating, Ventilation and Air Conditioning.

PURON - an environmentally sound refrigerant designed not to harm the earth's ozone layer. Federal law requires that all manufacturers phase out ozone depleting refrigerants in the next few years.

Refrigerant – a liquid used for heat transfer. It absorbs heat during evaporation (changing from a liquid to a gas) and releases heat during condensation (changing from a gas to a liquid)

Refrigerant Lines - copper lines used to transfer the refrigerant between the outdoor unit and the indoor unit.

SEER - Seasonal Energy Efficiency Ratio - measures the cooling efficiency of a heat pump or air conditioner. The higher the number, the more efficient the unit.

Split System - a refrigeration or air conditioning system in which the condenser and evaporator are in separate locations, joined by refrigerant piping.

Thermidistat – monitors indoor/outdoor temperatures and indoor humidity and adjusts system operation to maintain the temperature and humidity levels set by the homeowner.

Thermostat – a temperature control device, usually on a wall inside your home.

Ton – measures the rate of heat transfer. One ton is the equivalent of 12,000 BTUs per hour.

Upflow - describes the direction of airflow through a furnace. An upflow furnace takes cool air from the bottom, heats it, and delivers the warmed air out the top.

Ventilation - the process of moving air into and out of a space either by natural or mechanical (forced) means. Such air may or may not have been conditioned.

Zone/Zoning - A home may be divided into several different areas, or zones, to enable you to better control the temperatures in these areas. The process of dividing your home into different zones is called zoning.