Data logger

An electronic device that records data over time or in relation to location either with a built in or external instrument or sensors. In home energy auditing, they may be used to monitor various data points, such as temperature, water, humidity, gas flow, power, solar radiation, and wind.


Removing water vapor from air.

Dew Point Temperature

Water vapor at saturation; 100% RH; colloquial: temperature at which water begins to condense out of air onto a surface.


Device installed over openings in room surfaces created for Air-flow that aspirates room air, causing it to mix with the air stream; normally used in ceilings; always a Supply; damper or shutter for regulating Airflow is described separately.


(1) The movement of individual molecules through a material. The movement occurs because of concentration gradients (and to a much lesser degree) thermal gradients, independent of airflow. A mode of water vapor transport in building enclosures that is much slower than airflow. (2) is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion.

Drainage Plane

Drainage planes are water repellent materials (building paper, housewrap, foam insulation, etc.) which are designed and constructed to drain water. They are interconnected with flashings, window and door openings, and other penetrations of the building enclosure to provide drainage of water to the exterior of the building. The materials that form the drainage plane overlap each other shingle fashion or are sealed so that water flow is downward and outward.

Dry bulb temperature

Ordinary air temperature; as opposed to wet bulb temperature.


Conduit through which air is transported; normally modified by state of air as in Supply Duct, Return Duct, etc.

Duct Blaster

a blower-door-like device used for testing duct leakiness and air flow in a forced air heating or cooling system.