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. For example: A rating of 90 means that approximately 90 percent of the fuel is used to provide warmth to your home, while the remaining 10 percent escapes as exhaust.

BTU– British Thermal Unit. This is the amount of heat it takes to raise one pound of water one degree Fahrenheit. For your home, it represents the measure of heat given off when fuel is burned for heating or the measure of heat extracted from your home for cooling.

CFM– 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 on BTUs.

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 in cooling and provides warmer air during heating start up.

Compressor– 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.

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, it absorbs heat from the outdoors.

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.

Ductwork– Pipes or channels that carry air throughout your home. In a home comfort system, ductwork is critical to performance ­ in fact, it's as critical as the equipment.

Evaporator Coil or Indoor Coil– The other half of your air conditioning system located inside your home in the indoor unit. This is where the refrigerant evaporates as it absorbs heat from the air that passes over the coil.

Gas Furnace Heat Exchanger– Located in the furnace, the heat exchanger transfers heat to the surrounding air, which is then pumped throughout your home.

HSPF– Heating Seasonal Performance Factor. This rating is used in measuring the heating efficiency of a heat pump. The higher the number, the more efficient the unit.

Package Unit– A heating and cooling system contained in one outdoor unit. A package unit is typically installed either beside, on top of the home, or sometimes in the attic.

Refrigerant– A chemical that produces a refrigerating effect while expanding and vaporizing. Most residential air conditioning systems contain R-22 refrigerant. R-22 is regulated by international controls under the Montreal Protocol and in the United States by the Environmental Protection Agency. It is scheduled to be in production until the year 2020. It's used in approximately 95 percent of air conditioning equipment manufactured in the U.S. today.

SEER– Seasonal Energy Efficiency Ratio. A measure of cooling efficiency for air conditioners and heat pumps. The higher the seer, the more energy efficient the unit. The government's minimum SEER rating is 10. (It's similar to comparing miles per gallon in automobiles.)

SEET– Seasonal Extreme Environmental Test Lab. This is Trane's torture chamber for heating and air conditioning systems, where five years of service are condensed into 16 torturous weeks. If a product doesn't make it through our SEET lab, it's not manufactured. We push our equipment to extremes because we'd rather test them in our lab than in your home.

Split System– The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler). Split systems must be matched for optimum efficiency.

Thermostat– A thermostat consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system.

Ton– A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.

Zoning– A method of dividing a home into different comfort zones so each zone can be independently controlled depending on use and need.