How blower door tests work

A basic blower-door system includes three components: a calibrated fan, a door-panel system, and a device to measure fan flow and building pressure.

The blower-door fan is temporarily sealed into an exterior doorway using the door-panel system. The fan is used to blow air into or out of the building, which creates a small pressure difference between inside and outside. This pressure difference forces air through all holes and penetrations in the building enclosure. The tighter the building (e.g. fewer holes), the less air is needed from the blower door fan to create a change in building pressure.

Blower-door air-tightness measurements are presented in a number of different formats, including but not limited to:

Air flow
CFM50 is defined as the air flow (in cubic feet per minute) needed to create a 50-pascal pressure change in the building envelope. CFM50 is one of the most basic measurements of air-tightness. Air flow measurements are sometimes referenced to different building pressures such as 25 or 75 pascals.

Air changes per hour at 50 pascals
In order to compare the relative air-tightness of buildings, it is useful to normalize the measurements for the size of the building. This allows easy comparison of various sized buildings to each other, or to program guidelines. One of the most common ways to normalize building air-tightness is to calculate the number of times per hour that the total volume of the enclosure is changed, when the enclosure is subjected to a 50-pascal pressure difference. To calculate air changes per hour, the total volume of the enclosure is required in addition to the CFM50 measurement. It is also common to use the building enclosure surface area to normalize air-tightness measurements.

Leakage area
Leakage area estimates are a useful way to visualize the cumulative size of all leaks or holes in the building enclosure. Estimated leakage areas can also be used in infiltration models to estimate natural infiltration rates (i.e. the air change rate under natural weather conditions). In order to accurately estimate leakage areas, it is best to conduct the blower-door test over a wide range of building pressures (e.g. 60 Pa to 15 Pa). There are a variety of standard calculation methods used to calculate leakage areas. (Wikipedia, 2009)