The air tightness of a house is one of the most critical elements in its energy performance. Low-energy and low-carbon schemes such as PassivHaus, Super E®, Energy Star in North America and Minergie in France, all require an air leakage test to be done on houses before they are certified. In more and more countries in the EU, air leakage tests will be required for all new homes. Air leakage is measured using an air depressurisation test, also called a blower door test.
Elements of a blower door
A blower door has three main parts: a calibrated fan capable of inducing a range of air flows; a pressure measurement instrument called a manometer; and, some kind of mounting unit that can connect the instrument to a door in an air tight fashion. The unit is connected to a computer which takes the manometer’s readings and calibrates them.
Blower doors can be used to test air leakage in ducts, between different parts of a building, and overall air leakage to the outside of a building. The most common use is to test the overall air leakage of a whole building.
How the test is conducted
The machine is connected temporarily to an exterior door, then all exterior doors and windows are closed, interior doors opened and all vents and dampers closed. Ventilation fans are turned off. The fan is used to exhaust air from the building, putting it under negative pressure. The more air-tight the building (i.e. fewer holes), the less air will be required to depressurise the house to a preset measure. Usually, the measure is 50 Pascals of pressure. This is a relatively high pressure, approximately the equivalent of a 40 kmh wind blowing on all exterior surfaces of the house, but a high pressure is preferred to minimise the effect of wind. Blower door tests will provide inaccurate results if conducted on a particularly windy day.
Once the computer makes its air flow calculation, it is compared to the volume of the house. The most common measurement unit for air leakage is Air Changes per Hour. In other words, if the entire air volume of the house is required to hit test pressure in an hour, that would be 1.0 air changes per hour (ACH).
What is the right air tightness?
Various eco housing schemes set air tightness targets – generally ranging from 0.6 ACH (PassivHaus) to 3.0 ACH (Energy Star). There is no agreement as to what the “ideal” air leakage rate should be, although anything under 3 ACH signifies a potentially energy efficient house. Air tightness testing is also used as a measure of quality assurance. The depressurisation test identifies any unwanted leaks or cracks in the house, and if a test is run before the interior finish is applied, they can be fixed. The test can also determine the air tightness of windows and how well the window has been installed. Air tightness testing is becoming common in Europe, where the EU has set out a standard, EN 13829, which is based on the internationally recognised ISO 9972.