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What is a blower door test? And why is it important?

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Good Details from the architect and hard work from the contractor pays off!

You may have heard this term lately with all the new energy regulations around housing. A blower door test is a test of how air tight your house is. The reason you want an air-tight house is so that when you warm or cool the air in your house to be comfortable you don’t want it to leak out and waste your hard-earned energy dollars! Air tightness is as important as high R-values in the wall. You can have all the insulation in the walls you want, but if warm air is leaking out through cracks in the house, it doesn’t matter. Remember air is everywhere, so even the tiniest of cracks can make a difference.

So how is a blower door test done? A technician comes and puts a red tarp in an exterior door and runs a fan. The fan can either suck air into the house (pressurization test) or pull it out (depressurization test) We just completed a blower door test for a passive house this week. By measure the pressure difference between the interior and exterior of the house and knowing the volume of air in the house the technician can tell you how much air is leaking in and out. Blower door test results are measured in “air changes per hour” (ACH). This is the measure of how many times in an hour your house leaks all the air inside of it!


Both layers of insulation are taped over the joints to ensure air tightness. As well as timber penetrations and other penetrations are foamed.


The average house in Ontario leaks 6.5 times per hour!(1) Now this includes all homes old and new, but even new houses have a hard time meeting the building code minimum of 3.1 ACH! A note for new home buyers; if the builder has taken a prescriptive   path in the code they are not required to do a blower door test to ensure they are meeting this target. It is just assumed, so ask for it, it doesn’t cost more than $500. Low energy standards like Passive House and Net Zero require much more stringent standards. Passive house requires 0.5ACH, which is aggressive.

As a blower door test is being conducted you can go around the enclosure and find leaks and seal them up with spray foam, tape, or combination of materials. This test can be done on new houses or old houses. Common leak areas are around window frames, poor sealing patio doors, eaves, HVAC, plumbing and electrical penetrations to the exterior enclosure, eaves, rim joists, top of foundation walls, etc. Everywhere where there is a joint in the material you chance a leak.


See the air space at the bottom of the patio door? Patio doors are notorious for leaking!

VELD architect and Hulshof Carpentry are happy to report that the Wartburg residence met the passive house requirement! We celebrated with champagne and orange juice at our site meeting this morning!


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