Airflow Volume

The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper airflow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.

Air-Leakage (Air Infiltration)

The amount of air leaking in and out of a building through cracks in walls, windows, and doors.

Air-Leakage Rating

A measure of the rate of air-leakage around a window, door, or skylight in the presence of a specific pressure difference. It is expressed in units of cubic feet per minute per square foot of frame area (cfm/sq ft). Formerly expressed as cubic feet per minute per foot of window perimeter length (cfm/ft) but not now in use. The lower a window's air-leakage rating, the better its airtightness.

Allergen

A substance that induces allergic reaction.

Ambient Air

The air surrounding an object.

Ambient Temperature

The temperature of the air within a room or zone. (see environmental temperature).

Amp (Ampere)

The practical meter-kilogram-second unit of electric current that is equivalent to a flow of one coulomb per second or to the steady current produced by one volt applied across a resistance of one ohm.

Amp/Ohm/Volt Meter

Measures motor amperage and voltage test controls.

Ampere

The rate of flow of electricity through electric wires.

Annealed Glass

Standard sheet of float glass which has not been heat-treated.

Annealing

Heating above the critical or recrystallization temperature, then controlled cooling of metal, glass, or other materials to eliminate the effects of cold-working, relieve internal stresses, or improve strength, ductility, or other properties.

ANSI

American National Standards Institute. Clearing house for all types of standards and specifications.

Apartment

A separate room or suite of rooms in a building occupied by one party. Many of these apartments form apartment blocks, or blocks of flats.

Approved

Judged to meet or exceed specified standards

Architecture

The product, created in the process of applying art and science in the designing buildings.

Argon

An inert, nontoxic gas used in insulating glass units to reduce heat transfer.

Argon Filled

New vinyl windows are complete with double panes that have argon gas, a low conductive gas, between the panes for insulation to improve or omit the draft from the window glass. An improvement that can be made to the thermal performance of insulating glazing units is to reduce the conductance of the air space between the layers. Originally, the space was filled with air or flushed with dry nitrogen just prior to sealing. In a sealed glass insulating unit, air currents between the two panes of glazing carry heat to the top of the unit and settle into cold pools at the bottom. Filling the space with a less conductive, more viscous, or slow-moving gas minimizes the convection currents within the space, conduction through the gas is reduced, and the overall transfer of heat between the inside and outside is reduced.

ARI

An acronym for the Air Conditioning and Refrigeration Institute

ASHRAE

An acronym for the American Society of Heating, Refrigerating and Air Conditioning Engineers.

ASTM

American Society for Testing and Materials. Organization that sets standards for testing of materials.

Atrium

A open space in the middle or at the edge of a building, usually enclosed, but still allowing the penetration of light.

Attic

Accessible space between roof rafters and ceiling joists.  A low story or structure above the main part of a dwelling. Alternatively known as a loft or roof space.

Attic Access

A provision to gain access to an attic could be a scuttle hole, a pull-down stairway or hatch

Attic Ventilators

Openings in a roof or in gables that allow for air circulation.

Automatic Safety Controls

Devices designed and installed to protect systems and components from excessively high or low pressures and temperatures, excessive electric current, loss of water, loss of ignition, fuel leaks, fire, freezing or other unsafe conditions.

Average

A value which is typically used to sum up or describe a mass of data. It is a measure of central tendency. An average condition given its age and function, may need repair or replacement in the reasonable near future, showing definite signs of wear and/or usage.

Awning Window

A type of window having a sash with hinges at the top, which permit the window to open horizontally, forming an awning over the opening. Window similar to a casement except the sash is hinged at the top and always swings out.

Axial Or Vane Axial Fan

A fan in which the airflow, at all times, from entry to exit is predominately parallel to the axis of rotation.

Back Band Casing

A common or butt casing with molded and/or mitered trim piece around its outer edge.

Back Flow Preventer

See check valve

Back Pressure

The pressure in low side of refrigerating system also called suction pressure or low side pressure.

Back Seating

Fluid opening/closing such as a gauge opening to seat the joint where the valve stem goes through the valve body.