Glossary

Air Conditioning and Heating Terms

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Heat

A form of thermal energy resulting from combustion, chemical reaction, friction, or movement of electricity. As a thermodynamic condition, heat, at a constant pressure, is equal to internal or intrinsic energy plus pressure times volume. 

Heat Loss

The heat that flows from the building interior, through the building envelope to the outside environment. 

Heat Rate

The ratio of fuel energy input as heat per unit of net work output; a measure of a power plant thermal efficiency, generally expressed as Btu per net kilowatt-hour. 

Heat Register

The grilled opening into a room by which the amount of warm air from a furnace can be directed or controlled; may include a damper. 

Heating Capacity (Also Specific Heat)

The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree. 

Heating Degree Day(s) (HDD)

The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating system sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average temperature(s). 

Heating Load

The rate of heat flow required to maintain a specific indoor temperature; usually measured in Btu per hour. 

HEPA

High efficiency particulate arrestance (filters). 

Home Energy Rating Systems (HERS)

A nationally recognized energy rating program that gives builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise evaluation of energy losing deficiencies in homes. Builders can use this system to gauge the energy quality in their home and also to have a star rating on their home to compare to other similarly built homes. 

Hot Air Furnace

A heating unit where heat is distributed by means of convection or fans. 

Humidifier

A device for increasing the humidity in a room or home. 

Humidity

A measure of the moisture content of air; may be expressed as absolute, mixing ratio, saturation deficit, relative, or specific.

HVAC

HVAC is an acronym for heating, ventilation, and air-conditioning system

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