What is a blower door test?

Me: Are you having a blower door test done?

You: What does that even mean?  Is that a thing I need to think about?  I mean I feel draughts from under my front door and my bathroom is freezing because the exhaust fan lets in tonnes of air… and as soon as I turn my heater off my house is freezing again within minutes.  Is this a thing that I can measure??  And improve?

Me: Lend me your ears.


If you have excessive air leakage in your home, this creates a lot of discomfort.  This air also brings excessive heat or cold, moisture, bugs and rodents, and even excessive sound so assessing your air tightness can lead to many improvements in comfort and peace of mind.

You can test the air tightness of your home with a blower door test.

What is a blower door test?

A blower door test is an easy, repeatable test that can be performed on any house using a transportable fan kit and adjustable frame.  The timelapse below shows you the setup process.


  • The house is put under negative or positive pressure
  • The air required to create a 50 pascals pressure difference between inside and outside is recorded using a manometer and a laptop
  • A score is given, usually in Air Changes per Hour, or ACH for residential homes.

When you ask someone to come and do a blower door test, they will ask you for a few bits of information.  They will calculate the volume of your house for you but to do this, they will need a copy of your building plans.  If you don’t have plans, they will need to do a site measure.  This might cost you a bit of money as it takes time on-site before the test starts to take these measurements.

You will book a date and time for the blower door test to go ahead and in the lead up to this date, your blower door tester will keep an eye on the weather.  If the weather on the date is too windy or too hot, this will affect the outcome of the results and they may ask to reschedule to a date that is more suitable.

Climasure blower door test

If the weather is good, your blower door tester will arrive on-site with their equipment which looks like the equipment in the image to the left.  They will set it up in an external door – usually the front door but sometimes the garage door, the laundry door or another suitable doorway positioned in a protected area out of the wind.  Sliding doors are not suitable for the blower door setup.  If you have particularly high doors, above 2.7m, please make your tester aware.  They should pick this up by looking at your plans, but sometimes they may not and they will need to bring additional equipment for very high doors.

Before the fan is turned on, your tester will make sure that all external doors and windows are closed and all internal doors are open.  If your house is a new build, and not quite finished (e.g. electrical sockets may still be incomplete, or door seals may not yet be installed), they will need to tape these up to simulate the results of a complete house (see images to the right).

If you have too many unfinished items, your tester may prefer to come back on another day when the house is closer to completion as this taing can become very time-consuming.  Also the tape does not always stick properly when the house is under negative pressure and can skew results.

Once your tester has fully prepared the house for testing, they will turn the fan on and commence your blower door test.  They first take a pre-test baseline reading, then several air flow readings at different pressures, then a post-test baseline reading.  Once the test is complete, if they have worked out your volume and/or envelope area of your house ahead of time, they will be able to give you a result on the spot.

It can also be a fun and very informative activity to turn the fan back on once the test is complete, at a consistent pressure of say, 40 pascals, and do a thorough inspection of air leaks.  This is done by walking around the entire house and checking each junction, window, plumbing and electrical penetration, door seal, chimney, cavity sliding door, gas heater and exhaust fan for air leaks.  Often we use a small smoke pen or even a larger smoke machine for these inspections, but something as simple as a ribbon or strip of 1 ply toilet paper can be used to visually identify airflow.  You simply hold your chosen detective device in front of the air stream and watch it dance.  The other option is an anemometer which will give you an actual wind speed in m/s.

Your air tightness tester may also bring a thermal camera with them which will be used to identify thermal bridges, missing insulation and air leakage.   The images below show air leakage from around a dog door (left) and missing insulation batts (right).

Why should I have a blower door test done?

Air tightness is the underpinning element of thermal comfort and energy efficiency.  You can buy expensive windows and put in high levels of insulation, but if you have excessive air leakage you are significantly reducing the effectiveness of both of those things.

You may be wondering if this is something you have to do and the answer is no.  A blower door test is not yet a requirement for new construction in Australia, it is completely voluntary.  However, this testing has made its way into the code as an “optional” way to verify air tightness and we will likely, at some point, follow our international counterparts and introduce mandatory testing in some way.  But in 2023, we still have some time to get our heads around what a blower door test is.

What is a good level of air tightness?

Without mechanical ventilation – between 3 and 6 ACH is the “sweet spot”.

With mechanical ventilation – how low can you go…. There is no such thing as too low if your building is mechanically ventilated however 0.6ACH is the Passivhaus target.

What do I do after the blower door test?

Depending on what air leaks were found and what your score is, you may be able to make some easy improvements such as sealing up behind electric or gas heaters, adjusting door seals etc.  Talk to your tester about your results.

If you’d like to book a blower door test you can now do so online so head to our website www.climasure.com.au 

Chat soon!




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