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DIY blower door test?

This page describes how to build a DIY blower door:


Basically you use a furnace blower and a cheap magnetic or tube-of-water manometer. You can't finely tune the speed of the blower like a professional blower door, but given the few built-in speeds of the motor, you can generally find a speed that yields close enough to 50Pa that you can extrapolate the CFM50.

I have a furnace fan already sitting around from my decommissioned oil furnace, and I just bought a Dwyer Magnahelic manometer on Ebay for $15. Is this crazy or should it really work as described?

Asked by Nick Welch
Posted Aug 21, 2014 5:07 PM ET


2 Answers

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As long as you plan to use for the first two purposes described in the article -- to "find air infiltration leaks into your house" and to "trace your progress in sealing the house" -- this approach should work just fine.

I don't think that this set up would be accurate enough to extrapolate a cfm50 number at 50 pascals. But accuracy isn't particularly important for the two purposes under discussion.

Answered by Martin Holladay, GBA Advisor
Posted Aug 22, 2014 9:34 AM ET


Thanks Martin. Finding leaks is easy with any big enough fan. I was really interested in being able to track my progress and see the air leakage number go down as I seal things up. I realize it won't be accurate enough for me to go around boasting about my CFM50 number, but as long as I can see relative improvements in some quantitative way without scheduling and paying for a professional blower door test, that is pretty awesome.

Answered by Nick Welch
Posted Aug 22, 2014 1:18 PM ET

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