ACH50 Air Tightness Calculator

ACH50 is the number of times a home's entire air volume leaks out per hour when the house is depressurized to 50 pascals. It's the standard benchmark for air tightness.

• <1.0: Passive House standard (very tight, requires mechanical ventilation).
• 3.0: 2021 IECC code for many climate zones.
• 5-7: Typical 2000s+ construction.
• 10+: Older homes — major air sealing opportunity.

• Seal the attic floor first — stack effect makes top-of-house leaks hurt the most.
• Spray foam rim joists in the basement.
• Caulk and gasket around plumbing and electrical penetrations.
• Weatherstrip exterior doors and replace failed window seals.
• Re-test with a blower door after sealing — most homeowners cut ACH50 by 30-50%.

Results are estimates based on typical conditions. Actual costs vary by climate, utility rates, equipment efficiency, and home characteristics. Use them as a starting point — for precise figures consult a qualified energy auditor or your utility company. Estimates are not a guarantee, and any work you do on your home is at your own risk — we are not liable for installation errors or property damage. Air sealing a home with gas, oil, propane, or wood-burning appliances can cause backdrafting and carbon monoxide risk — get a combustion safety test and keep CO alarms working. See our Disclaimer.