The following is a compilation of building energy-code related terms and acronyms used on the Building Energy Codes website and throughout the building construction industry.

Select a letter to navigate through the glossary:


A (23) B (23) C (41) D (27) E (28) F (15) G (12) H (21) I (20) K (5) L (11) M (16) N (15) O (11) P (21) R (22) S (37) T (14) U (12) V (11) W (10)

Voltages and currents at frequencies other than 60 Hz (or 50 Hz where applicable) that cause heating and other detrimental effects in the power system.


See Heating Degree Day Base 65F

Heat Capacity

The amount of heat necessary to raise the temperature of a given mass 1°F. Numerically, the sum of the products of the mass per unit area of each individual material in the roof, wall, or floor surface multiplied by its individual specific heat.

Heat Pump

One or more factory-made assemblies that include an indoor conditioning coil, compressor(s) and outdoor coil or refrigerant-to-water heat exchanger, including means to provide both heating and cooling functions.

Heat Trace

A heating system where the externally applied heat source follows (traces) the object to be heated, e.g., water piping.

Heat Traps

Devices or piping arrangements that effectively restrict the natural tendency of hot water to rise in vertical pipes during standby periods. Examples are the U-shaped arrangement of elbows or a 360-degree loop of tubing.

Heated Slab

Slab-on-grade construction in which the heating elements or hot air distribution system is in contact with or placed within the slab or the subgrade.

Heated Space

Space within a building that is provided with a positive heat supply (see "Positive Heat Supply"). Finished living space within a basement with registers or heating devices designed to supply heat to a basement space shall automatically define that space as heated space.

Heating Degree Day Base 65F

For any one day, when the mean temperature is less than 65°F, there are as many degree days as degrees Fahrenheit temperature difference between the mean temperature for the day and 65°F. Annual heating degree days (HDDs) are the sum of the degree days over a calendar year.

Heating Degree Days (HDD)

A unit, based upon temperature difference and time, used in estimating fuel consumption and specifying nominal heating load of a building in winter. For any one day, when the mean temperature is less than 65°F (18°C), there exists as many degree days as there are Fahrenheit degrees difference in temperature between the mean temperature for the day and 65°F (18°C).

Heating Seasonal Performance Factor (HSPF)

The total heating output of a heat pump during its normal annual usage period for heating, in Btu, divided by the total electric energy input during the same period, in watt hours, as determined by DOE 10 CFR Part 430, Subpart B, Test Procedures, and based on Region 4. Heat pump heating is expressed in terms of HSPF. New equipment ranges from about 6.8 to 10.0 HSPF. Higher HSPF ratings indicate more efficient equipment.


High-intensity discharge.

High-Intensity Discharge Lamp (HID lamp)

An electric discharge lamp in that light is produced when an electric arc is discharged through a vaporized metal, such as mercury or sodium. Some HID lamps may also have a phosphor coating that contributes to the light produced or enhances the light color.

High-Rise Residential Building

Hotels, motels, apartments, condominiums, dormitories, and other residential-type facilities that provide complete housekeeping or transient living quarters and are over three stories in height above grade. Hotels, motels, and other buildings with itinerant occupancies are covered by the "commercial" code regardless of height.


A building or space that has been specifically designated as historically significant by the adopting authority, is listed in "The National Register of Historic Places," or has been determined to be eligible for listing by the U.S. Secretary of the Interior.

Hot Water Supply Boiler

A boiler used to heat water for purposes other than space heating.


The U.S. Department of Housing and Urban Development.


A regulatory device, actuated by changes in humidity, used for automatic control of relative humidity.


Heating, ventilating, and air conditioning.

HVAC System

The equipment, distribution network, and terminals that provide either collectively or individually the processes of heating, ventilating, or air conditioning to a building.


A space or group of spaces within a building with heating and cooling requirements that are sufficiently similar so that desired conditions (e.g., temperature) can be maintained throughout using a single sensor (e.g., thermostat or temperature sensor).