Blower Door & Air Leakage Calculator | ACH50 & CFM Tool
Blower Door & Air Leakage Calculator – an interactive tool that estimates Air Changes per Hour (ACH50) from a blower door test result, or calculates the required CFM to achieve a target ACH
🌀 Blower Door & Air Leakage Calculator
Why Use This Blower Door & Air Leakage Calculator?
A blower door test measures how leaky a home is by depressurizing it and recording the airflow (CFM) needed to maintain 50 Pascals. This result is converted to Air Changes per Hour (ACH50) – the number of times the entire house air volume is replaced per hour under test pressure. Lower ACH50 means a tighter, more energy‑efficient home. Our tool helps you interpret blower door results or plan a sealing project.
Key Features
- Two modes: Calculate ACH50 from measured CFM, or find required CFM to hit a target ACH50.
- Adjustable house dimensions – length, width, ceiling height (volume auto‑calculates).
- Real‑time visual gauge and airtightness rating (Passive House to Very Leaky).
- Natural infiltration estimate (ACHnat ≈ ACH50 / 20).
- Rotating energy tips – learn about common air leaks and sealing benefits.
- Dark/light mode toggle – comfortable for any time of day.
Frequently Asked Questions (FAQ)
What is ACH50?
ACH50 is the number of air changes per hour at a pressure difference of 50 Pascals (Pa) – the standard test pressure for blower doors. It is the most common metric for residential airtightness.
How do I get my blower door CFM?
A certified energy auditor uses a blower door fan and manometer to measure the CFM required to maintain 50 Pa. Some utilities offer low‑cost or free blower door tests as part of energy efficiency programs.
What is a good ACH50 score?
- < 1.5 ACH50 – Passive House / extreme tightness
- 1.5 – 3 ACH50 – Excellent, very energy efficient
- 3 – 5 ACH50 – Good, typical new construction
- 5 – 8 ACH50 – Moderate, some air sealing recommended
- > 8 ACH50 – Leaky, significant savings possible
How do I reduce my ACH50?
Seal attic bypasses, rim joists, window and door frames, electrical outlets, and plumbing penetrations. Use caulk, spray foam, weatherstripping, and rigid air barriers. After sealing, re‑test to measure improvement.
What is natural infiltration (ACHnat)?
Under normal weather conditions (no wind, average temperature), the natural air change rate is roughly ACH50 divided by 20. For example, a home with ACH50 = 4 would have ACHnat ≈ 0.2, meaning the air is replaced completely every 5 hours under calm conditions.
Disclaimer: This tool provides educational estimates based on standard formulas. Always consult a certified energy auditor for official blower door testing and interpretation.
