Annual Fuel Utilization Efficiency. Indicated as a percentage, your furnace's AFUE tells you how much energy is being converted to heat. For example, an AFUE of 90 means that 90% of the fuel is being used to warm your home, while the other 10% escapes as exhaust with the combustion gases. The higher the AFUE, the higher the efficiency of your furnace.

Type of compressor that uses a more efficient process for compressing refrigerant for better cooling efficiency.

The portion of your air conditioner or heating system that forces air through your home's ductwork.

Air purifiers treat 100% of the air flowing through your HVAC system before it even circulates, removing particulates, bacteria and viruses from the air.

British Thermal Unit. Used for both heating and cooling, BTU is a measure of the heat given off when fuel is combusted. Or for cooling, it's a measure of heat extracted from your home. (One BTU is approximately equal to the heat given off by a wooden kitchen match.)

A British Thermal Unit (BTU) is the unit of heat required to raise 1 pound of water by 1 degree Fahrenheit. BTUH is British Thermal Units per Hour.

A burner assembly within your oil furnace, providing combustion for heating oil.

Cubic Feet per Minute. A measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system.

The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTUs. For cooling, it is usually given in tons.

A colorless, odorless, highly poisonous gas produced when carbon-based fuels, such as natural gas, burn without sufficient air.