HVAC Definitions

ACH (Air Changes per Hour) - The number of times per hour the entire volume of air is replaced in a given area. Per the Department of Energy, a maximum of three air changes per hour are allowed in our region.

AFUE (Annual Fuel Efficiency Ratio) – A measure of furnace efficiency at converting fuel to energy on a seasonal or annual basis. A higher AFUE rating indicates a more efficient a furnace. For example, an 85% AFUE rating indicates that 85% of the energy inputted into the furnace is used for heating.  

Air Handler – Also known as the indoor unit. It includes the evaporator coil, fan-blower and often the filter(s). It removes latent heat from a given area, thus “cooling” the area.

BTU (British Thermal Unit) – The quantity of heat required to raise the temperature of one pound of water by one degree Fahrenheit.

Condenser – Also known as the outdoor unit. It houses the condenser coil and compressor. In contrast to the evaporator, the condenser converts hot, high-pressure refrigerant into a cool, low-pressure refrigerant.

Duct – A channel that carries conditioned air throughout the building and unconditioned air back to the air handler.

EER (Energy Efficiency Ratio) – A measure of an air conditioner’s performance under specific test conditions. While SEER is calculated at a test temperature of 82°F and for the duration of the cooling season, EER can be calculated at any temperature for a specific day in the cooling season.

HSPF (Heating Seasonal Performance Factor) – Similar to the SEER, except for the heating season.  This measures how efficiently a heat pump operates throughout a heating season.

Load – The amount of cooling or heating required in a given area to maintain a specific temperature, measured in BTU/hr.

MERV (Minimum Efficiency Reporting Value) Rating – A performance indicator used to measure an air filter’s effectiveness, based on a scale of 1-20. Most homes and offices use filters with a MERV rating ranging from 5 to 12.

Package Unit – A type of HVAC system that contains both the air conditioner and air handler in one unit (“self-contained”). They are primarily placed outdoors and are ideal for commercial rooftops or homes without basements.

Preventive Maintenance – The act of performing periodic HVAC maintenance to mitigate the likelihood of future problems through system inspection and cleaning. By having quarterly maintenance performed, HVAC technicians are able to catch and fix minor system issues before they turn into major and expensive repairs or replacements.

Refrigerant – Any substance used to dispel heat from a conditioned area to one that is unconditioned.

Return Air – The air removed from a conditioned space back to the air handler to be re-conditioned.

SEER (Seasonal Energy Efficiency Ratio) – An estimate of the average efficiency of an air conditioner throughout the entire cooling season. A higher rating should result in more energy savings because the unit is operating more efficiently. An air conditioner must have a SEER rating of 15 or higher to qualify for the EPA’s Energy Star program. The drawbacks of the SEER ratio are highlighted in our FAQs section.

Split System – A central HVAC System in which the condensing unit and evaporating unit are housed separately.

Supply Air – Conditioned air leaving an air handler and headed to an area.

Tonnage – The metric used to measure a system’s cooling capacity. One ton is the equivalent of 12,000 BTU/hr.

Zone System – A type of HVAC system that allows for different temperatures in different areas, or zones, of a building. This is performed with the use of a zone control, zoning dampers and zone thermostats.

The Single Source for all your Commercial and Industrial HVAC needs. 

Miller HVAC Service, Inc.

306 East Frontage Road, Greer, SC 29651

License # M112685

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