Energy Advisors, Auditors, & Evaluators all rely on a blower door to gauge the performance of new & existing housing.

The Blower Door, Explained

Shawna HendersonJanuary 30, 2018

One of the key ways to measure and quantify how well a house will perform in terms of both energy efficiency and comfort is the blower door test. You can benchmark, quantify, and compare blower door test results. It’s a fairly reliable way of determining the air leakage rate in a house or a multi-unit building.

Analog magnehelic gauge used in blower door testing




The blower door has four main parts to it. An adjustable frame, an impermeable skin that attaches to the frame, a large fan, and a set of magnehelic gauges, which measure both the fan pressure and air velocity across the fan. I worked with analog gauges - new equipment is all digital. 


The door frame and skin are installed in the main entry, then the fan is turned on and depressurizes the house. The gauges measure how hard the fan has to work (the fan pressure) to move a measured volume of air (air velocity in cubic feet per minute) across the fan. With these two measurements and the measured volume of the house, you can learn a lot about how the house or building performs - and how to improve it.


The blower door is used to measure air leakage rates, and is also used to diagnose air leakage problem areas. It can also measure the amount of air connection between adjoining units. This helps identify poorly sealed party (shared) walls between dwelling units that lead to transfer of odours, or between the living space and a garage, which can lead to exhaust fumes being pulled into the home. With an infrared camera, the blower door can also help you clearly identify thermal bypasses that are hidden behind wall and floor finishes, or leakage areas in places you can’t actually reach, like high ceilings.


Here’s an excellent three part video from Montana Weatherization Training Center that really does a good job of showing the set up, testing and tear down of a blower door. Each video is about 15 minutes long.

A couple of notes:

  1. The host is using a Minneapolis Blower Door™ unit from The Energy Conservatory. That’s the unit that I worked with, so I’m kinda partial and a little sentimental. Retrotec is the other industry standard.

  2. The unit he’s using has DG-700 gauge. That unit was discontinued as of November 2017, and all new equipment comes with the DG-1000 gauge. The functions for testing are the same, because the test protocols haven’t changed, but the DG-1000 is a touch screen unit. TEC has stated that they will calibrate DG-700 gauges for the next 5 years or so, if you’ve got one.

  3. Canadian and US testing protocols vary, but this is a great introduction to the whole set up, walk through, and tear down. Check out my Jan 2018 article on the concerns around the CGSB test.


The blower door is a versatile piece of equipment. It’s one of my favourite performance testing/diagnostic tools and ranks high up there with all the good teaching tools.


The most gratifying days are when a homeowner is there with you, and the blower door is on. It really showcases the need for air sealing and how air leakage impacts comfort levels. There’s been so many times I’ve watched people’s eyes go wide and they get it: this is where the room is cold, this is where I’m uncomfortable because of a draft. It’s a great jumping off point for a ‘teachable moment’ in building science.


As an R2000 tester and inspector, and then as an early Energy Advisor, I used the blower door daily for many years, even lugging it up a full set of front stairs while 8 months pregnant (ya, that was really a lot of fun). I think the guys on site were taking bets that I might drop the baby right then and there. Or possibly that I might hit them with the fan if they came too close to me after not offering to help. Either way, they stood way back and observed while I wrestled the fan (and the belly) to the porch. Life as theatre…

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