Blower Door Testing

Every home has air leaks, but the cumulative amount of leaks can vary widely based on the air sealing efforts. Infiltration and air sealing basics are covered in part 1 of this post.
To measure the amount of leakage in a home we use a tool called a blower door, which is comprised of a calibrated fan, a mounting system to attach the fan to an exterior door, and a manometer which measures pressure.
To understand the principle behind the blower door test imagine a large parade balloon like Kermit here. If the balloon is completely air tight we can pressurize it, shut off the valve, and the balloon will remain inflated indefinitely.
Now imagine the balloon has some small leaks at the seams. To keep it inflated we need to continuously blow in air to replace the air leaking through the seams. The larger the leaks are, the more air is required. Thus, if we can measure the amount of air we are blowing into the balloon to keep it fully inflated, we can infer how leaky the balloon is.
That’s exactly what a blower door test does: it measures the amount of air needed to keep a house at an elevated pressure of 50 Pascal (i.e. “inflated”), and we use that measurement to infer how many leaks are present.