ACH50 to Natural ACH Calculator
Estimate natural infiltration ACH from a blower door ACH50 result.
Enter your values
ⓘ Live results
Results
- Estimated natural ACH
- 0.25
- n-factor used
- 20
- Air changes per day
- 6
Quick answer
Natural ACH is estimated by dividing the tested ACH50 by an empirical n-factor that reflects climate, building height and shielding.
ACH_natural = ACH50 / n
How to use the ACH50 to Natural ACH Calculator
- 1Enter the ACH50 result from a blower door test.
- 2Choose an n-factor appropriate for the climate, building height and exposure (20 is a common simplified default).
- 3Read the estimated natural (non-pressurized) infiltration rate.
Worked example
Using the values the calculator loads with:
Inputs
- ACH50 from blower door test5.0
- n-factor (climate/height)20 - Typical (LBNL default)
Results
- Estimated natural ACH0.25
- n-factor used20
- Air changes per day6
Frequently asked questions
Is 20 always right?
No — it is a widely-used simplification; taller and more exposed buildings often use a lower n-factor (more infiltration per ACH50).
Why do I need natural ACH at all?
Natural ACH better represents everyday infiltration for load calculations than the test-pressure ACH50 figure.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.