HVAC Dictionary

Definitions for common HVAC terms: A&Ks HVAC Dictionary

Our HVAC dictionary provides explanations for terms and abbreviations that are common in HVAC industry.

Understanding basic, efficiency and technical HVAC terms are important especially when comparing new equipment. Higher efficiency units generally achieve significant energy cost savings over the long term.

HVAC: Heating, Ventilation, Air Conditioning

HVAC/R: Heating, Ventilation, Air Conditioning, Refrigeration

AFUE: Annual Fuel Utilization Efficiency. AFUE is a measure of a furnace’s heating efficiency. A higher AFUE percentage means a more efficient product.
Air Handler The portion of a central air conditioning or heat pump system that moves heated or cooled air throughout a home’s ductwork. In some systems, a furnace handles this function.
Balance Point: An outdoor temperature – usually between 30°F to 45°F – at which a heat pump’s output exactly equals the heating needs of the house.
Below the balance point, supplementary electric resistance heat is needed to maintain indoor comfort.
British Thermal Unit (BTU): The amount of heat required to raise the temperature of one pound of water (about one pint) by one degree Fahrenheit.
Defrost Mode: During the heating cycle of a heat pump, frost may build up on the outdoor coil. To remove the frost and maintain efficiency, the system will automatically defrost itself. This usually only takes a few minutes, then the system automatically switches back to heating. It is normal to see steam rising from the outdoor unit when this happens.
Ductless Split System: Ductless split systems are the ideal air conditioning and heating solution for installations where adding duct work is impractical or too expensive. The matched combination of an indoor air handler and outdoor condenser is extremely efficient and reliable. The indoor units can be mounted on almost any wall. Ductless air conditioners and heat pumps offer a higher efficiency than traditional systems. And they do this with less noise, and no costly duct work! Ductless split systems are also called Mini-Split Systems.
EER: Energy Efficiency Ratio. A ratio calculated by dividing the cooling capacity in Btu’s per hour (Btuh) by the power input in watts at a given set of rating conditions, expressed in Btuh per watt (Btuh/watt). (See Seasonal Energy Efficiency Ratio, above.)
Heat Source: A body of air or liquid from which heat is collected. In an air source heat pump, the air outside the house is used as the heat source during the heating cycle.
HSPF: Heating Seasonal Performance Factor. HSPF is a measure of a heat pump’s heating efficiency. The higher the HSPF rating, the more efficient a heat pump is at heating your home.
Indoor Coil: The portion of a heat pump or central air conditioning system that is located in the house and functions as the heat transfer point for warming or cooling indoor air.
Kilowatt (kW): A kilowatt equals 1,000 Watts. A kilowatt hour (kWh) is the amount of kilowatts of electricity used in one hour of operation of any equipment.
Mini-Split System:  A Split System that uses physically smaller indoor and outdoor units than standard Split Systems.  Also referred to as Ductless Split Systems. Read more about Ductless Split Systems
Multi-Split System: A type of Ductless Split System that connects up to five indoor units to a single outdoor unit with no need for duct work. A complete air conditioning system to multiple zone interior spaces. Provides individual control of room temperature settings.  Enables indoor units of different styles and capacities in one system for customized solutions unique to each residential setting.
Outdoor Coil/Condensing Unit: The portion of a heat pump or central air conditioning system that is located outside the home and functions as a heat transfer point for collecting heat from or dispelling heat to the outside air.
SEER: Seasonal Energy Efficiency Ratio. SEER is a measure of cooling efficiency for air conditioning products. The higher the SEER rating number, the more energy efficient the unit.
Split System: Most residential HVAC systems are Split Systems.  They are referred to as Split Systems because they typically have an indoor unit and an outdoor unit. Indoor units include furnaces or air handlers while outdoor units are usually a condensing unit, which is better known as an air conditioner. The air conditioner cools the air and sends it to the indoor unit. The indoor unit then circulates the cool air through your home.
Supplementary Heat: The auxiliary or emergency heat provided at temperatures below a heat pump’s balance point. It is usually electrical resistance heat. Also known as the heater package. But supplemental heat can also be gas or oil – fired equipment.
Ton: Heat pumps and air conditioners are generally sized in tons. Typical sizes for single family residences are between two and five tons. Each ton equals 12,000 Btuh. It is important to note that actual capacity is not constant and will change based on outdoor or indoor temperatures. The published capacity rating of air conditioners and heat pumps is based on performance at the ARI standard temperature levels of 95 F outside, 80 F inside.
Watt (W): A Watt is a unit of electricity.
Zone: A zone is the area that one thermostat is controlling. For example: A two story house with a thermostat on each floor has two zones, one for each floor.

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