To install an exhaust fan without backdraft, first seal all gaps between the fan and housing using high-quality caulk and weatherstripping. Ensure the ductwork is airtight by applying mastic sealant around joints and screws. Install a backdraft damper or止回阀 (translated to "check valve") in the ductline to prevent reverse airflow. Position the fan at least 12 inches above the vent opening to align with natural airflow patterns. Test the system by running the fan and inspecting for air leaks using a thermal leak detector or incense stick. If backdraft occurs, reapply sealants or adjust the damper.

Backdraft occurs when outdoor air infiltrates a home through exhaust systems, reducing ventilation efficiency and increasing energy costs. A 2020 study by the U.S. Environmental Protection Agency (EPA) found that improper exhaust fan installation leads to 10–30% energy loss annually due to air leakage. The Department of Energy (DOE) estimates that backdraft can raise heating and cooling bills by $200–$500 yearly. Airtight sealing reduces moisture buildup, which the EPA links to 85% of crawl space mold cases. ASHRAE Standard 62.1 mandates airtight duct systems to maintain 0.01–0.02 air changes per hour. Using a backdraft damper, as recommended by HVAC experts, blocks 95% of reverse airflow (Energy Star, 2021). Neglecting these steps risks health hazards and financial losses, with 40% of U.S. homes experiencing backdraft-related issues (DOE, 2019). Proper installation aligns with building codes and ensures compliance with energy efficiency standards.