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.

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.

Condensor 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.)

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.

Ten Time-Proven Tips For Selecting A Dealer

1. Check credentials. Before making your selection, call the Better Business Bureau to make sure the dealer is reputable. Also, find out if the dealer is a member of a local or national association such as the Air Conditioning Contractors Association of America.

2. Make sure the dealer is affiliated with a nationally known manufacturer. Dealers should be taking advantage of factory training offered by their manufacturer. As a result, when they make recommendations, you can be more assured that they've selected the right size system for your home, and that they've been trained in installation and service.

3. Ask for references. Former customers are an excellent source of information. Also, ask to see installation photos. A dealer that is proud of work will be more than happy to show it to you.

4. Expect an on-site evaluation of your home. A good dealer will take a thorough look at your home, ask questions and evaluate your overall comfort needs before making a recommendation. Beware of a dealer that simply takes information over the phone. A good dealer will also look the part. While he's evaluating your home, you should be evaluating him. Not only should he dress professionally, but his truck and printed materials should look professional as well.

5. Check local licenses. Depending on where you live, dealers may have to comply with certain local or state regulations, so ask to see proof of these licenses as well as insurance forms for liability and workmen's compensation.

6. Don't be afraid to ask questions. Ask for details about the firm's experience and the expertise of its staff. This is particularly important if you're also adding or changing ductwork ­ in this case, experience is definitely a factor in getting the job done correctly.

7. Get a written proposal. To make a fair comparison, make sure the proposals you receive are all based on the same efficiency and equipment. You'll also want to evaluate each dealer's personal business standards and policies. For example, will he remove old equipment? Will he relocate equipment if you want your new system installed in a different location? What are his clean up and care policies during installation? How will he handle emergency repair? These are just a few of the additional elements a good proposal will include.

8. Inquire about equipment and labor warranties. Limited warranties vary according to the manufacturer, so make sure you fully understand what you're getting. Also, don't forget to inquire about manufacturer's extended warranties at the time of purchase and other warranties provided by the dealer.

9. Ask about preventive maintenance service agreements. Many dealers offer service agreements that call for periodic maintenance of equipment, and if needed repairs. The fee for such agreements is usually well worth it in terms of obtaining optimum efficiency and performance for your system.

10. Finally insist on a written agreement. Commit your agreement to writing and have the dealer sign it.