Convert a blower door result into air changes per hour and an airtightness rating.
The blower door measures leakage at an artificial 50 pascal pressure, and dividing by volume gives a figure comparable between houses of different sizes. Natural infiltration is roughly a twentieth of the ACH50 result. Air sealing is normally the cheapest efficiency measure per unit of energy saved, and it must come before insulation because leaks bypass insulation entirely.
Home Energy Audit
ACH50 = blower door flow at 50 Pa ÷ building volume
ACH50 = blower door flow at 50 Pa ÷ building volume The blower door measures leakage at an artificial 50 pascal pressure, and dividing by volume gives a figure comparable between houses of different sizes. Natural infiltration is roughly a twentieth of the ACH50 result.
Air sealing is normally the cheapest efficiency measure per unit of energy saved, and it must come before insulation because leaks bypass insulation entirely.
This calculator takes 4 inputs: Blower door result, Floor area, Average ceiling height, Target air changes at 50 Pa. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.