What is a blower door?


A blower door is a nylon panel set in an adjustable frame with a fan inserted. A pressure gauge measures the difference in pressure inside and outside and can also calculate the flow of air through the fan. It can either pressurise or depressurise the building to a set pressure difference and then calculate how much air is being moved to maintain that pressure difference. There are various ways to report the result but the most commonly used is the air changes per hour at 50 pascals (ACH@50Pa). This is roughly the pressures exerted on a house in a pretty windy day.

Baw Baw Sustainability Network won a federal gov’t grant for half the purchase price of this bit of technology and we are using it to great effect in our home sustainability assessments. While the blower door is operating it is easy to go around the home and detect the sources of air leaks, either with your hand (even better if it’s wet) or with a thermal imaging camera which can show visually where the leaks are. It is also very useful to have the door operating as we go around draught proofing the house with caulking, draft stoppas, weather seals and the like so you can tell how effective the work is being.

Many countries have enforceable standards for air leakage in new buildings. Typically they range from 3 to 5 ACH@50Pa and the building must be tested with a blower door to prove it meets the standard. In Australia, our building code is very lax in comparison. There is no requirement for air tightness, no performance testing and very little awareness of the problem. Consequently, our housing stock is relatively poorly performing in terms of energy efficiency. It is not uncommon to hear people who have come from Europe exclaim that they have never been as cold in their life as they have been in their Australian home. CSIRO, Moreland Energy Foundation and others have done studies to find the average ACH@50Pa in Australian homes and the results vary from 15 to 29. Take a house at 20ACH and consider that means on a cold, windy day the whole of the air in the house is being turned over every 3 minutes. If you are trying to heat that air to stay comfortable, your heater is going to be going like the clappers to keep up and you are paying through the nose to do so. It’s easy to see why draught proofing is the place to start to get control of your energy bills.

We are keen to see better building standards for Australia and to have performance based testing as well with mandatory reporting of the results when the dwelling is purchased or leased. That way home buyers and renters can quickly tell if they are in for an energy guzzling, uncomfortable home or one that is cosy and cheap to run. You can join the push for this change by joining the Rental Standards project at Environment Victoria, tell your friends, write letters to the paper and politicians and even better- start work on your own home now.


2 thoughts on “What is a blower door?

  1. When my solar-passive house was being built in 1998, I wanted to have it tested with a blower door. I could not find one at all at that time. I had to simply do my best to make sure that no leaks were allowed to persist. I think I did reasonably well.
    Recently, I had an automated louvre installed to improve night purge ventilation. Again, there was some doubt about the draft-proofing, and a blower door would have been handy. My louvre project was discussed in an Alternative Technology Association forum thread:

    In that thread I linked to my blog page about my house:

    You kindly posted a comment on a post on my blog called “Solar-passive house testimonials” saying that you liked it. I’m glad that struck a chord with you.


  2. Hi Surlybond, we live in a strawbale and rammed earth house that performs well in winter and summer as I see yours does. I have never been diligent enough to get into the temperature recording and reporting though! We do have one issue affecting the performance and comfort- the shading on the north side. The eave rakes up to the north and was left only wide enough to shade the summer sun. Shading for autumn sun relies on ornamental grapes over the pergola and as they are still growing, they are not doing the job yet. There’s a piece of temporary shadecloth but that is not enough. I suppose a fixed shading device might have been smarter but I like the feeling of interconnectedness between life/garden and the house. In another couple of years I will know if the plan works!


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