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To have a better understanding of some of the terms in our industry, here is a glossary of the most common and key terms:


AFUE
Annual Fuel Utilization Efficiency. Used to express the efficiency of gas furnaces. The higher the AFUE rating, the more efficient the unit.

AIR HANDLER
A central unit consisting of a blower, heating and cooling elements, filter racks or chamber, dampers, humidifier, and other central equipment in direct contact with the airflow. This does not include the ductwork through the building. Abbreviated AH or AHU.

BTU
British Thermal Unit. The amount of heat required to raise or lower the temperature of one pound of water by one degree Fahrenheit.

BTUH
The heat transfer rate of HVAC equipment is 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 20-ton air conditioning unit has twice the capacity of a 10-ton unit.

CFM
A unit to express movement of volume, including air, in Cubic Feet per Minute. A 400 CFM air handler moves 400 cubic feet in one minute.

COIL
Equipment that performs heat transfer to air when mounted inside an air handling unit or ductwork. It is heated or cooled by electrical means or by circulating liquid or steam within it.

COMPRESSOR
The compressor plays an integral role in cooling 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.

CONDENSER
The coil responsible for dissipating heat to the surrounding, outside air. Also called the condenser coil, or outdoor coil, its role is reversed when a heat pump is used in heating mode.

COP
The Coefficient of Performance 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.

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.

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 the Air Conditioning and Refrigeration Institute specifications.

EVAPORATOR OR EVAPORATOR COIL (INDOOR)
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
Responsible for transferring heat from furnace burners to the blower. Rheem uses some of the finest heat exchangers in the industry with limited lifetime warranties on some models.

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

HEAT LOAD, HEAT GAIN, HEAT LOSS
Terms for the amount of cooling (heat gain) or heating (heat loss) needed to maintain desired temperatures and humidities in controlled air. Regardless of how well-insulated and sealed a building is, buildings gain heat from sunlight, conduction through the walls, and internal heat sources such as people and electrical equipment. Buildings lose heat through conduction during cold weather. Engineers use a heat load calculations to determine the HVAC needs of the space being cooled or heated.

HSPF
Heating Seasonal Performance Factor. It measures the efficiency of the heating portion of your heat pump. The Department of Energy minimum is 6.8. (Similar to SEER.)

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.

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

HEAT PUMP 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 at the same time.

KILOWATT
A unit used to express 1,000 Watts. Denoted as "kW." Note that the "W" in "kW" is always capitalized because the Watt unit was named after a person.

KWH
If a unit uses 1,000 Watts in 1 hour, it is said to have an energy rating of 1kWh.

MODULATING FURNACES
Furnaces are designed to deliver maximum heat for comfort on the coldest of days. In most cases, those days account for fewer than three percent of winter days. The rest of the time, your furnace is providing more heat than necessary.
Because conventional furnaces are either providing no heat, or at full capacity, the temperature in your house goes up and down by several degrees, adversely affecting your comfort and your energy bills.
Modulating furnaces solve this problem by varying the amount and temperature of air delivered between different capacities, so that the air flowing out of the registers is always at the temperature you determine. This results in lower operating costs, more comfortable temperatures throughout the house and quieter operation.

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
Copper lines used to transfer the refrigerant between the outdoor unit and the indoor unit.

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. The Department of Energy minimum is 13 SEER.

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 SRNs of between 74dB and 80dB.

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
The ton ratings you see here have nothing to do with the weight of the unit. In fact a ton is simply 12,000 BTUs (see BTU definition on this page). A typical home cooling/heating system uses heat pumps or air conditioners with a capacity of between 1.5 and 5 tons.

VAV
Abbreviation for variable air volume. An HVAC system that has a stable supply-air temperature, and varies the air flow rate to meet the temperature requirements. Compared to constant air volume systems, these systems conserve energy through lower fan speeds during times of lower temperature control demand. Most new commercial buildings have VAV systems. VAVs may be bypass type or pressure dependent. Pressure dependent type VAVs save energy while both types help in maintaining temperature of the zone that it feeds. .

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.

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.