Glossary

Vapor Retarder

A material that retards the movement of water vapor through a building element (walls, ceilings) and prevents insulation and structural wood from becoming damp and metals from corroding. Often applied to insulation batts or separately in the form of treated papers, plastic sheets, and metallic foils. 

Variable Air Volume System (VAV)

Air handling system that conditions the air to constant temperature and varies the outside airflow to ensure thermal comfort. 

Vent

A component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space. 

Vent Damper

HVAC term for a device mounted in the vent connector that closes the vent when the heating unit is not firing. This traps heat inside the heating system and house rather than letting it draft up and out the vent system. 

Vent Pipe

A tube in which combustion gases from a combustion appliance are vented out of the appliance to the outdoors. 

Vented Heater

A type of combustion heating appliance in which the combustion gases are vented to the outside, either with a fan (forced) or by natural convection. 

Ventilation

The process of moving air (changing) into and out of an interior space either by natural or mechanically induced (forced) means. 

Ventilation Air

Defined as the total air, which is a combination of the air brought inside from outdoors and the air that is being re-circulated within the building. Sometimes, however, used in reference only to the air brought into the system from the outdoors; this document defines this air as “outdoor air ventilation.” 

Ventilation Rate

The rate at which indoor air enters and leaves a building. Expressed in one of two ways: the number of changes of outdoor air per unit of time (air changes per hour, or “ach”) or the rate at which a volume of outdoor air enters per unit of time (cubic feet per minute, or “cfm”).