What is the purpose of a blower door test in an HVAC system?

The purpose of a blower door test in an HVAC system is to measure the airtightness of a building envelope and quantify air leakage, which directly impacts heating and cooling load, comfort, indoor air quality, and energy efficiency. A blower door is a powerful fan temporarily mounted in an exterior door frame that depressurizes the house to 50 Pascals and measures airflow in cubic feet per minute needed to maintain that pressure, revealing how leaky the house is. For HVAC, this information is critical because the amount of air leakage determines how much outside air infiltrates and how much conditioned air escapes, affecting sizing of heating and cooling equipment, duct leakage testing, and ventilation requirements. A leaky house may need larger HVAC equipment and will have drafts, uneven temperatures, high bills, and moisture problems, while a very tight house below 3 air changes per hour at 50 Pascals needs mechanical ventilation like an ERV or HRV to provide fresh air. The test also helps locate leak locations using smoke pencils and infrared cameras, guiding air sealing improvements that reduce load and improve HVAC performance and comfort.