Before you do any air sealing, have a home energy pro test your home’s airtightness and look for air leaks. Your home’s airtightness should be tested

  • before you start remodeling, to establish the baseline of air leakage in your home and to help locate its sources;
  • during the remodeling work, to identify and seal new leaks; and
  • after remodeling is done, to document the improvement resulting from the air sealing.

The tool for testing air leakage in your home is called a blower door. A home energy pro can use it to quantify the air leakage rate of a house.

The basic principle of blower door operation is simple. A powerful fan, set temporarily in a doorway, creates a pressure difference between the house and the outdoors, usually by depressurizing the house. All the air the fan blows out of the house is replaced by air coming in through leaks. 

So all we need to do is measure the house pressure and the amount of air moving through the fan, and—voilà—we know how much the house leaks at that test pressure. Airflow is measured in CFM, and the pressure normally used for this test is 50 pascals (Pa, a measure of pressure differential). Hence, home energy pros in the United States use the notation CFM50 or CFM@50Pa—which is about equal to the pressure of a 20 mph wind.

A blower door can also be used for diagnosis, by running the blower and walking around the house to find leaks by hand, using a smoke pencil (see photo to the left) or a thermal-imaging (infrared) camera.

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