Heating and Air Conditioning Glossary

AFUE - Annual Fuel Utilization Efficiency, a rating that reflects the efficiency of a gas furnace in converting fuel to energy. A rating of 90 means that approximately 90% of the fuel is utilized to provide warmth to your home, while the remaining 10% escapes as exhaust. If your furnace was built before 1992, chances are it is operating with an average efficiency of around 60%. Most of the heat is lost up the chimney or out the exhaust vent - devices used by older furnaces to expel dangerous fumes created by the furnace, such as carbon monoxide, carbon dioxide, aldehydes, and even soot. Modern furnaces use more technologically advanced venting techniques to achieve greater energy efficiency. An important note: Be sure to ask your installing contractor if your chimney or exhaust vent is suitable for use with your new equipment.

ARI - The Air Conditioning and Refrigeration Institute is an organization created by HVAC manufacturers to ensure an acceptable level of quality within the industry. ARI is a voluntary, nonprofit organization which publishes ratings standards and benchmarks for testing 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 the equivalent of the heat given off by a single wooden kitchen match. 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.

BTUH - The heat transfer rate of measured in British Thermal Units per Hour.

CAPACITY - Usually measured in BTUs or tons, capacity refers to an air conditioning or heating unit's ability to cool or heat a space. For instance, a 4-ton air conditioning unit has twice the capacity of a 2-ton unit.

CFM - A standard of airflow measurement in volume. Cubic feet per minute. A typical system produces 400 CFM per ton of air conditioning. A 400 CFM air handler moves 400 cubic feet in one minute.

COMPRESSOR - The heart of an air conditioning or heat pump system. The compressor plays an integral role in cooling or heating your home. It is the device responsible for pumping refrigerant through the refrigerant lines and the coil, making the transfer of heat from inside your house to the outdoors possible or in the case of a heat pump transferring heat from outdoors and the compressor to the inside of your home.

CONDENSER COIL OR OUTDOOR COIL - Located in the outdoor unit, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid. Its role is reversed when a heat pump is used in heating mode. In American Standard units, the coil is either Spine FinTM or Plate Fin.

COP - The Coefficient of Performance (COP) rates a heat pump's ability to efficiently use electricity in its operation. The Air Conditioning and Refrigeration Institute provides the Coefficient of Performance at 47 degrees Fahrenheit and 17 degrees Fahrenheit. This is because a heat pump is more efficient at higher, outside-air temperatures.

DAMPER - Found in duct work, this movable plate opens and closes to control airflow. Dampers are used effectively in zoning to regulate airflow to certain rooms. dB The relative loudness of a sound is expressed in dB, short for decibel. As an example, the sound of a human voice talking is around 70 dB. (See also SRN.)

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

DOWNFLOW - A term used to describe the direction of airflow through a furnace. A downflow furnace takes return air from the top, heats it, and then delivers the warm air expelling it out the bottom of the unit.

DUCT / DUCTWORK / DUCTING - A central heating and air conditioning system uses many components to heat or cool air. This warm or cool air is then transferred to different registers throughout the house via special, flexible, large-diameter pipes or ducts. The system of ducts throughout your house is often referred to as ductwork or ducting.

EER - Energy Efficiency Ratio. The ratio of the cooling capacity of the air conditioner in BTUs per hour to the total electrical input in watts. This measure is determined by comparing test units to ARI specifications.

EFFICIENCY - A general term used to describe how effectively a heat pump, air conditioning system, or furnace converts energy in to energy out. The higher the number, the more efficient the unit, and the lower the operating costs.

EVAPORATOR COIL / EVAPORATOR - An integral part of the indoor unit of a heat pump or air conditioning system. So called because when warm air passes over a coil filled with liquid refrigerant, the refrigerant itself evaporates and absorbs some of the heat. This gas refrigerant is then pumped to the outdoor coil, where it releases heat into the surrounding air and returns to its liquid state.

HEAT EXCHANGER - A device for the transfer of heat energy from the furnace burners to the air from the blower.

HORIZONTAL FURNACE - A term used to describe the direction of airflow through a furnace. A horizontal flow furnace takes return air from one end, heats it, and then delivers the warm air to the other end.

HUMIDIFIER - Usually available as an optional accessory, a humidifier is used to inject water vapor into the dry, heated air expelled from a furnace/air handler. The benefits can be improved efficiency and a more comfortable living environment.

HUMIDITY - The amount of moisture in the air. Air conditioners remove moisture for added comfort.

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

HVAC - Heating, Ventilating and Air Conditioning. Used to refer to the industry at large, particularly dealers of heating and air conditioning equipment.

IAQ - Indoor Air Quality. The air inside your home is usually more polluted than the air outside. That means millions of unwanted airborne particles are being inhaled by you and your family. Particles like pollen, dust, bacteria, tobacco, smoke, cooking smoke, animal hair and dander keep your indoor air from being as clean and healthy as it could be. And if anyone in your family suffers from asthma or allergies, the quality of the air in your home is even more important.

INDOOR COILS - Split-system home comfort systems use two main components to deliver air for a comfortable living environment. The indoor coil is the device responsible for transferring heat from indoors to the outdoors (or the reverse in the case of a heat pump in heating mode). Most modern systems are designed to achieve maximum efficiency when the indoor unit (coils and blower) is properly matched with the outdoor unit (air conditioner or heat pump). For best results, be sure to replace both the indoor and outdoor units.

ICM - Integrally Controlled Motor. A specially engineered, variable-speed motor used in top-of-the-line indoor units. ICM motors are more than 90% efficient versus 60% efficiency for conventional motors. Continuous comfort, whisper-quiet operation and ultimate system efficiency are the benefits of the indoor products graced with the ICM motor. An ideal motor for efficient filtration for the best in Indoor Air Quality(IAQ).

MODULATING GAS FURNACES - The most advanced furnace technology available today. This break through technology can keep temperatures throughout your house constant. As constant as one-half of one degree of your thermostat setting. The fan speed and heat output are automatically and constantly varied. The result is that air flows from the registers at the precise temperature you select, for lower utility bills and greater comfort.

PACKAGE UNIT - Equipment in which all heating and cooling components are located in one cabinet. Installed either beside or on top of a home or business.

REFRIGERANT - The liquid used to absorb and transfer heat from one part of the home comfort system to another.

REFRIGERANT LINES - Set of two Copper lines used to transfer the refrigerant between the outdoor unit and the indoor unit. Some times referred to as the line set.

SEER - Seasonal Energy Efficiency Rating. Used to express the efficiency of an air conditioning unit, or a heat pump in cooling mode. The higher the SEER rating, the more efficient the unit.

SPLIT SYSTEM - A home comfort system that uses an indoor and an outdoor component to deliver comfortable air to a living environment.

SRN - The Air Conditioning and Refrigeration Institute performs tests and assigns a Sound Rating Number (SRN) to units. A lower SRN rating indicates a quieter unit with average SRN's of between 74dB and 80dB.

SWITCHOVER VALVE - A device in a heat pump that reverses the flow of refrigerant as the system is switched from cooling to heating. Also called a reversing valve or four-way valve.

THERMOSTAT - A temperature-measuring device used to control the operation of home comfort systems to maintain a comfortable temperature within the house. Programmable thermostats allow you to program different temperatures for different times of the day.

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

WATT / WATTS - Electrical power, also expressed as 'W'. For example, a 100W globe consumes 100 Watts of electrical power. The W in Watt is always uppercased, because it is named after a person. KWH If a unit uses 1,000 Watts in one hour, it is said to have an energy rating of 1kWh.

UPFLOW - A term used to describe the direction of airflow through a furnace. An upflow furnace takes return air from the bottom, heats it, and then delivers the warm air from the top.

ZONE / ZONING - A home may be divided into several different areas, or zones, to better control the temperatures throughout the house. The process of dividing your home into different zones is called zoning.