The Blower Door Test

There are certain things that one takes for granted in life, and for me, one of those things has been paying PG&E for the gas and electricity it takes to keep our house warm in the winter, and presently, to keep the trailer cool here in the heat of the north bay summer.

One of my favorite things is turning up the thermostat when its cold out, but I never really thought about it beyond anticipating how great that burst of warmth is going to feel.  I didn’t wonder about why it was necessary in the first place – it just seemed like a fact of life that if it was cold out, it would get cold inside, and if it was hot out, it would get hot inside.

But, as it turns out, this doesn’t need to be a fact of life – houses can be constructed (or retrofitted!) in a way that makes them much more insulated from the outside environment.  This is, of course, the main point of Passive House – and one of the ways it is accomplished is by drastically limiting the amount of air leakage from the house.

Most of us might think about poorly sealed doors and windows as a source of air leaks, or maybe a fireplace, but there are other, less obvious culprits that also add up – these come from all of the places you can imagine something has been “cut” into the walls, roof, or floors of the house – plumbing, electrical, venting, or that time you drilled a hole through the wall to tie into your neighbor’s cable service.

Since eliminating these leaks is such a critical component of Passive House, there is (of course) a standardized way to measure exactly how much air is leaking out of a given building, and there is (of course) a specific measurement that needs to be achieved in order to get Passive House certification.  As you might have guessed by now, this is measured by the Blower Door Test.

Our test was administered by Steve Mann of Home Energy Services.  Steve is our Passive House and LEED certifier, energy adviser, and an important part of our team. Here is Steve attaching the door blower, which is literally a fan in a housing that is attached very snugly to a door.









Ready to Go:


I’m not going to try to explain how this test actually works, because there is a great explanation on this page here and I strongly encourage you to go read it now – it will only take a second, it doesn’t require any technical background, and it’s got Kermit the Frog, so you know it’s good.

Once everything was set up, the test went really quickly.  And the results were pretty much as we all expected – the house as it stands today is very, very drafty!  Now, the actual test result is here:


But this number, alone, doesn’t tell us the amount of air leakage as a proportion to the size of the house – which is an important element of the final number and required to get a standardized score.  If you want to totally geek out on Passive House calculations for air leakage, and get way more in depth than the Kermit page, you can do that here.

The above measurement resulted in a final score of 19.7 for us (“living in a barn” according to the Kermit page), and we knew that is roughly what we’d be looking at.  This is the “before” test, after all.  For context, this equates to a 5.5 square foot sized window being open all the time!  The score we need to achieve for Passive House certification is just 0.6 – so there is a long way to go, but that is the work we’re so excited about doing.  We’ll likely do another test as we get to a certain point in the construction, and of course at the end of the project to get our final score for certification.

If you have any questions on The Blower Door test, ask them in the comments – I think we might be able to get Steve to answer them!

One thought on “The Blower Door Test

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