LOCATING AIR LEAKS

“Identify air leakage paths and reduce heating costs
by removing unwanted draughts”

To obtain meaningful data about the tightness of a building shell, Airtightness tests are performed on finished houses. All exterior openings such as doors and windows are closed, thereby simulating a heating season configuration.

As part of this test we use a blower door fan.  When operating, the blower door fan acts as an exhaust fan and vents indoor air to the outside. This sucking action causes the air pressure in the house to drop below the pressure of the air outside.

Detecting air leaking into the conditioned space is a simple matter of feeling for leaks around openings such as window trim, can lights, or heat registers, to name just a few of the possible sources of air leaks. Alternatively, a smoke-generating device can be used to make leakage paths visible.

The ability to detect leaks with one’s hands or by means of a smoke-generating device works on the principle that what goes out (through the exhaust fan) must come in through the enclosure. An operating blower door turns all of the leaks in the building envelope into leakage paths for infiltrating air. All of the intentional openings (fireplaces with the dampers closed, fan ducts, etc.) as well as all unintended openings contribute to the total measured air leakage.

The blower door system
The system consists of a powerful, variable-speed fan with a speed controller mounted in an adjustable panel that is temporarily fit into an open exterior doorway. A set of manometers or differential pressure gages are used to measure pressure differences generated by the fan. Airflow across a calibrated opening in the fan housing is also measured

Measuring Air Leakage
Blower door testing is usually performed in a depressurization mode. As air is exhausted out of the house (or building envelope), the house becomes depressurized relative to the air pressure outside the house. Expressed in pascals (a pascal or Pa is a unit of pressure), the magnitude of the difference between these two pressures will depend upon the capacity of the fan because it works against the backpressure created across the building envelope.