A blower door test is a diagnostic tool used to measure the air leakage in a building. It involves installing a powerful fan in an exterior door frame, which creates a pressure difference between the inside and outside. This helps identify how much air is escaping and where the leaks are located. The results of a blower door test can help homeowners and builders improve energy efficiency by sealing leaks. By reducing air infiltration, buildings can maintain comfortable temperatures and lower energy costs, making them more sustainable and cost-effective over time.