What is a Blower Door Test?
Written by Andrew Champness
A Practical Guide for Architects, Engineers, and High-Performance Buildings
A blower door test is a diagnostic test used to measure how airtight a building is. It identifies how much air leaks through the building envelope (the walls, ceilings, floors, windows, doors and service penetrations that separate the inside of a building from the outside).
The test uses a large specialist and calibrated fan temporarily installed in an external doorway. This fan either pressurises or depressurises the building, creating a pressure difference between the inside and outside. Sensors then measure how much air the fan must move to maintain that pressure.
The more air required to maintain pressure, the leakier the building.
What Does a Blower Door Test Measure?
The result of the test is typically expressed as Air Changes per Hour at 50 Pascals (ACH50).
This number represents how many times the total air volume inside the building is replaced in one hour under the test pressure.
As a general guide:
10 ACH50 = very leaky building
5 ACH50 = typical older construction
3 ACH50 or lower = good modern construction
0.6 ACH50 = Passive House standard
Lower numbers indicate a tighter, more energy efficient building envelope.
Why Does Airtightness Matter?
- higher heating and cooling costs
- reduced indoor comfort
- moisture entering the building structure
- poor indoor air quality
When Is a Blower Door Test Performed?
Blower door testing is typically performed:
- during construction to identify leaks early
- at completion to verify airtightness performance
- for energy efficiency verification
- for high-performance buildings such as Passive House
As building standards continue to evolve, blower door testing is becoming an increasingly important tool for verifying construction quality and energy performance.
Everything You Need to Know About Blower Door Test
Everything You Need to Know About AS 2252 in Australia
Everything You Need to Know About ISO 14644
Get Expert Advice for Your Next Project
As energy costs rise and government projects demand measurable outcomes, airtightness has become a core performance metric.
Whether you are targeting NABERS ratings, Green Star certification, or standard NCC compliance, getting the details right at the design stage is non-negotiable.
Need airtightness testing for compliance or project verification? Submit the form and our team will reach out to you shortly.