Blower Door Test

Blower Door Test

A blower door test quantifies how much air leaks through your home's envelope—walls, ceiling, windows, doors, and penetrations. A powerful fan mounts in an exterior door frame and depressurizes the house to 50 Pascals, simulating a 20 mph wind on all sides. Pressure gauges measure the airflow required to maintain this pressure, calculating air changes per hour (ACH50). Lower numbers indicate tighter homes with less wasted energy. Testing with a smoke pencil or thermal camera during depressurization pinpoints specific leak locations.

Why It Matters for Energy Efficiency

Air leakage causes 25-40% of heating and cooling losses—often more than poor insulation. Modern energy codes increasingly require blower door testing, typically targeting 3-5 ACH50 for new homes. Air sealing before adding insulation dramatically improves performance and return on investment. In San Diego's climate with 6,000+ heating degree days, reducing air leakage saves significant energy costs. Testing identifies priorities: seal attic penetrations, rim joists, and window/door rough openings before adding insulation.

Common Test Results

• Excellent: 1-2 ACH50 (passive house level)
• Good: 3-4 ACH50 (modern energy code)
• Average: 5-7 ACH50 (typical existing homes)
• Poor: 8+ ACH50 (older, leaky homes)
• Common leak locations: Attic hatches, recessed lights, rim joists, window/door frames
• Post-test improvements: Air sealing with caulk, foam, and weatherstripping