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)

Time rate of steady-state heat flow through the unit area of a material or construction surfaces. Units of C-Factor are Btu/h x ft2 x degrees Fahrenheit. Note that the C-factor does not include soil or air films.


The Council of American Building Officials.

Cavity Insulation

Insulation installed between structural members such as wood studs, metal framing, and Z-clips.


Cooling degree day. See "Cooling Degree Days."


Cooling degree days base 50°F. See "Degree Day Base 50F."


Combustion efficiency.


The ceiling requirements apply to portions of the roof and/or ceiling through which heat flows. Ceiling components include the interior surface of flat ceilings below attics, the interior surface of cathedral or vaulted ceilings, skylights, and sloped building assemblies less than 60 degrees from horizontal, but excluding skylight shafts.


Cubic feet per minute. A standard measurement of air flow.

Check Metering

Measurement instrumentation for the supplementary monitoring of equipment and tenant energy use (electric, gas, oil, etc.) in addition to the revenue metering furnished by the utility.

Circuit Breaker

A device designed to open and close a circuit by non-automatic means and to open the circuit automatically at a predetermined overcurrent without damage to itself when properly applied within its rating.

Circulating Water Heater

Hot water continuously circulates through the distribution system.

Circulation Pumps

Pumps that are used to keep hot water circulating through the distribution system.

Class of Construction

For the building envelope, a subcategory of roof, above-grade wall, below-grade wall, floor, slab-on-grade floor, opaque door, vertical fenestration, or skylight.


That part of a building that rises clear of the roofs or other parts and whose walls contain windows for lighting the interior.

Coefficient of Performance (COP)

The ratio of the rate of heat removal to the rate of energy input, in consistent units, for a complete refrigeration system or some specific portion of that system under designated operating conditions.

Color Temperature

The absolute temperature (in degrees kelvin) of an incandescent blackbody radiator that radiates the red-orange end of the spectrum. Higher color temperatures are near the blue-violet end of the spectrum.

Commercial Building

Includes but is not limited to occupancies for assembly, business, education, institutions, merchants, and storage.

Compact Flourescents

Small fluorescent lamps that are often used as an alternative to incandescent lighting. The lamp life is about 10 times longer than incandescent lamps and is 3 to 4 times more efficacious.

Compact Fluorescent Lamp

A fluorescent lamp of a small compact shape, with a single base that provides the entire mechanical support function.

Concrete Masonry Unit Walls

Concrete masonry unit walls may be insulated by filling the empty core with perlite, vermiculite, or some other insulative material. In some cases, even with filled cores, these wall types require additional insulation.

Condensing Unit

A specific refrigerating machine combination for a given refrigerant, consisting of one or more power-driven compressors, condensers, liquid receivers (when required), and the regularly furnished accessories.

Conditioned Floor Area

The horizontal projection of that portion of interior space that is contained within exterior walls and that is conditioned directly or indirectly by an energy-using system.

Conditioned Space

A space is conditioned if heating and/or cooling is deliberately supplied to it or is indirectly supplied through uninsulated surfaces of water or heating equipment, uninsulated ducts, or uninsulated floors, ceilings, or walls between it and another conditioned space.

Connected Lighting Load

The sum of all non-exempt interior lighting power, measured in watts.


The fabrication and erection of a new building or any addition to or alteration of an existing building.

Construction Documents

Drawings and specifications used to construct a building, building systems, or portions thereof.

Continuous Insulation (CI)

Insulation that runs continuously over structural members and is free of significant thermal bridging; such as rigid foam insulation above the ceiling deck. It is installed on the interior, exterior, or is integral to any opaque surface of the building envelope.


To regulate the operation of equipment.

Control Device

A specialized device used to regulate the operation of equipment.

Cool Down

Reduction of space temperature down to occupied set point after a period of shutdown or setup.

Cooled Space

An enclosed space within a building that is cooled by a cooling system with a capacity that either: 1) exceeds 6 Btu per hour per square foot, or 2) is capable of maintaining a space dry-bulb temperature of 90°F or less at design cooling conditions.

Cooling Degree Days

A unit, based on temperature difference and time, used in estimating cooling energy consumption and specifying nominal cooling load of a building in summer. Cooling degree days (CDD) are calculated by subtracting 65°F (18°C) from the mean temperature of any given day that has an average temperature that is over 65°F (18°C).

Cooling Design Temperature

The outdoor dry-bulb temperature equal to the temperature that is exceeded 1% of the number of hours during a typical weather year.

Cooling Design Wet-Bulb Temperature

The outdoor wet-bulb temperature for sizing cooling systems and evaporative heat rejection systems, such as cooling towers.

COP Cooling

The ratio of the rate of heat removal to the rate of energy input, in consistent units, for a complete refrigeration system or some specific portion of that system under designated operating conditions.

COP Heating

The ratio of the rate of heat delivered to the rate of energy input, in consistent units, for a complete heat pump system, including the compressor and, if applicable, auxiliary heat, under designated operating conditions.