Calculators · Consulting

Airtightness converter

n50 · q50 · air permeability · blower-door flow

Enter your building and one measured figure. We convert it to every basis a PHPP file, a blower-door certificate and a Part L submission need, then check it against the Passivhaus limit.

0.6 Passivhaus n50 limit, checked live

Exact the conversion is arithmetic, not an estimate

✓ the figures certifiers and auditors ask for

Your building

From the PHPP or the test report.

Internal volume, V_n50 m³, the air volume tested

Envelope area, A_E m², the air-barrier surface

What did you measure?

Air changes per hour at 50 Pa.

Converted, at 50 Pa

0.60ACH

n50, air-change rate0.60 /h

q50, air permeability0.46 m³/h·m²

V̇50, air flow at 50 Pa300 m³/h

Equivalent leakage area*– cm²

Meets the Passivhaus limit (n50 ≤ 0.6)

Get airtightness on the project

*Equivalent leakage area is indicative: estimated at 4 Pa with flow exponent n = 0.65 and discharge coefficient 1.0. The n50/q50/flow conversions are exact for the volume and envelope area you enter.

How it converts

Every metric is the same blower-door air flow on a different basis:

n50 = V̇50 ÷ V, air flow per unit internal volume (air changes/hour).
q50 = V̇50 ÷ A_E, air flow per unit envelope area (UK Part L air permeability).
So q50 = n50 × V ÷ A_E. Getting V and A_E right is the whole game.
Passivhaus tests against n50 ≤ 0.6 /h; EnerPHit allows ≤ 1.0. Part L is set as a permeability (q50) target.

Why trust it: these are the definitions in ISO 9972 / EN ISO 9972 and PHPP. Every airtightness strategy we issue is checked by one of our 7 accredited Passivhaus certifiers.

Take it further

Need an airtightness strategy that actually passes?

The number is easy. Hitting 0.6 on site is a detailing and sequencing problem. We set the line, detail the junctions and support the team to the test. Tell us about the project.