Building Science-Natural Air Leakage

This blog first appeared on the Green Building Advisor website.

When conducting a blower door test, one of the ways we express the findings is with air changes per hour at 50 Pascals (ACH50).  As an example, a new home is blower door tested and found to be 2.75 ACH50, this means the entire volume of air inside the home is exchanging with the outside air 2.75 time per hour at the test pressure of 50 Pascals.  When discussing blower door testing with builders and homeowners, it can be hard for them to relate to the ACH50 number other than they know the home needs to be less than a certain level of air tightness to meet current code requirements.  Expressing the tightness as natural air leakage can sometimes be helpful.  How can we calculate the natural air change rate?  Well, there’s a formula:

ACH50/n-Factor = ACHnat Continue reading “Building Science-Natural Air Leakage”