A blower door is a variable speed fan, mounted in a doorframe, used to pressurize and depressurize a house to measure air leakage. Many air leaks and drafts are easy to find because they are easy to feel — like those around windows and doors. But holes hidden in attics, basements, and crawlspaces are usually bigger problems. A certain amount of fresh air is needed for good indoor air quality and there are specifications that set the minimum amount of fresh air needed for a house.

If your home is too tight, a fresh air ventilation system may be recommended.