The ABCs of HVAC: A heating and cooling dictionary for homeowners
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As with any highly skilled trade, heating, ventilation and air-conditioning (HVAC) contractors and technicians have their own language. They use a variety of terms and concepts that most of us do not deal with on a daily basis. A good HVAC contractor will take the time to explain everything to you when performing maintenance or installing a new system, but it doesn't hurt to have some basic knowledge so that you can ask intelligent questions and ensure the efficiency of your equipment. Here's a list of some of the terms you may encounter.
AFUE—Stands for “annual fuel utilization efficiency.” It’s a rating of how well a furnace or boiler converts fuel into heat. The higher the AFUE, the more efficient the furnace or boiler.
ACH—Stands for “air changes per hour.” That’s the number of times the air in a given space, such as a house, is completely changed thanks to natural or mechanical ventilation.
Air filters—Placed on the return side of furnaces to remove dust, dirt and other debris from reaching the working parts of the furnace.
Air handler—The part of a heating and/or cooling system that is responsible for moving air through the ductwork.
Boiler—A unit that converts a fuel, such as natural gas, into hot water or steam for home heating.
BTU—An abbreviation of British Thermal Units, a measurement of heating or cooling capacity. You will see it as part of equipment descriptions. It is equal to the amount of heat it takes to raise one pound of water one degree Fahrenheit.
Coil—Part of the heat transfer system. There are two types of coils. In an air-conditioner or heat pump, an evaporator coil removes heat from the indoor air; the condenser coil removes heat from the system and is located outdoors. Because heat pumps provide both heating and cooling, the role of these coils can change.
Compressor—Located outdoors, the compressor converts a low-temperature, low-pressure refrigerant into a high-temperature, high-pressure refrigerant. This conversion aids the condenser in ejecting heat from the air-conditioning system.
Condenser—Part of a central air-conditioning system or heat pump that ejects heat from the system. The condenser is the outdoor part of a central air-conditioning system.
Dampers—Located inside ductwork, these plates direct air flow.
Ducts—A delivery system that carries cooled or heated air throughout the home.
Energy audit—A survey of the "energy package" of a home. The audit will include an examination of heating and cooling equipment, as well as insulation levels, types of windows, air infiltration and ventilation.
Energy Star—A joint program of the Department of Energy and the Environmental Protection Agency that rates a variety of appliances, including heating and cooling equipment. Energy Star products are more energy-efficient than typical models. Manufacturers that meet the requirements can place the Energy Star logo on their qualifying products.
Furnace—A heating unit that coverts a fuel, such as natural gas, into heated air.
Heat exchanger—A device that transfers heat from one medium to another. In a furnace, burners heat the heat exchanger, which is a series of tubes and coils. A fan blows air over the hot coils. The coils heat the air, which then flows through the home's ductwork.
Heat pump—An appliance that can switch between heating and cooling modes.
HSPF—Stands for “heating season performance factor.” It is used to describe the heating efficiency of heat pumps. SEER is a similar term that’s used to measure cooling efficiency (see below).
Humidifier—A device that adds moisture to the air as it travels from a furnace through the ductwork.
IAQ—Stands for “indoor air quality.” Tightly sealed houses need proper ventilation to avoid poor air quality.
Load calculation—A way to determine the amount of heating and cooling capacity a home needs.
Programmable thermostat—A control device that can alter the temperature settings of the heating and cooling system depending on the time of day.
Refrigerant—A heat-transfer fluid that circulates between the evaporator coil and the condenser in an air-conditioning system and heat pump. The compressor increases the temperature and pressure of the refrigerant before it reaches the condenser.
Return side—The part of an HVAC system that returns air from the home to the furnace or air conditioner. The return side should be balanced with the supply side.
SEER—Stands for “seasonal energy-efficiency ratio.” This is an energy-efficiency rating for air-conditioners. The higher the rating, the more efficient the product.
Single-package system—A unit that contains both heating and cooling components.
Split system—An air-conditioning system that contains both indoor and outdoor components.
Supply side—The part of an HVAC system that supplies heated or cooled air to the home. The supply side should be balanced with the return side.
Ton—Used in describing a cooling system's size. One ton equals 12,000 BTU.
Zoned system—A heating and cooling system that is divided into specific sections. For example, one zone may include the first floor of a house; another zone may cover the second floor. Each section is controlled by its own thermostat.
Once you understand the basic terms and concepts of heating and cooling, you’ll be able to communicate better with your contractor. You will also be more adept at determining which systems are more energy-efficient and keeping up with the status of your current equipment.
Home-improvement author Fran Donegan writes on home energy efficiency for The Home Depot. Fran’s tips on understanding heating and cooling terms are designed to help homeowners be more informed when considering repairs or replacement. Research on Home Depot services for heating and cooling is available online.
Companies: The Home Depot