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Community and Q&A

DIY blower door test – crazy?

Trevor Lambert | Posted in Energy Efficiency and Durability on

I am having trouble finding someone willing to do a blower door test. All the firms I have contacted have said they will only do a complete Energy Audit as part of the government rebate program. I’m guessing they get a kickback from the government on top of what they charge the homeowner. So I’ve resorted to thinking up a way to test it myself. If I build a frame that fits my door opening, install a blower motor in it, power it with a variac and adjust it until the pressure differential is 50Pa, then measure the flow with a flow hood and an anemometer, how close could I get to the accuracy of a commercial unit? Is it a hare brained scheme? I already have a suitable blower motor, and access to the other items. The only work would be building the frame.

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Yes, it's a hare brained scheme to re-engineer one of these things. A lot of engineering time & testing goes into making a calibrated blower door to get any accuracy. For a DIY hack with an anemometer you might get 1 significant digit accuracy on the cfm, maybe even 1.5 digits if you have a lot of experience with measuring things in an engineering environment, but probably not 2. It also gets tougher to be accurate as the air tightness of the house improves.

    The "government rebate program" is in most cases something already paid for by utility ratepayers, and the cost of running the audits are subsidized. It's usually a few hundred USD in setup & test time if doing it without subsidy, though sometimes weatherization contractors will give you a freebie or discounted "before" measurement as part of a proposal/bid on more work.

    If your goal is just to pressurize the house adequately to find & fix a bunch of leaks (rather than measure the accurate cfm/50 numbers) it's a more tractable problem. If you REALLY want to take semi-real measurements, are some useful pointers here:

    https://www.builditsolar.com/Projects/Conservation/BlowerDoor/BlowerDoor.htm

    https://www.builditsolar.com/Projects/Conservation/BlowerDoor/FlowRates.htm#BlowerFlow

    http://www.builditsolarblog.com/2013/02/a-inexpensive-diy-blower-door-that.html

    https://www.builditsolar.com/Projects/Conservation/BlowerDoor/UsingBlowerDoor.htm

    (Note: Gary Reysa has the experience advantage of his career in engineering.)

  2. GBA Editor
    Martin Holladay | | #2

    User-6792900,
    Can you tell us your name?

    As Dana Dorsett explained, it's very unlikely that you can build a blower door that will obtain results that are accurate enough to compare with a calibrated blower door from a company like the Energy Conservatory.

    But it is easy to build a blower door that works well enough to perform blower-door-directed air sealing -- and if that's your goal, you should go for it.

  3. Trevor Lambert | | #3

    I've fixed my screen name. I have no idea why it reverted to a generic name. I've since found a guy who will do the test for me, which is my preference. I'll build a blower door and do some leak finding if I don't get the results I expect.

  4. Trevor Lambert | | #4

    Thanks for the feedback. The site you linked is what gave me the idea that it might be possible.

  5. Lance Peters | | #5

    I have planned to do something similar. I have an inline duct fan ratedat 800 CFM and I think it would work well for finding leaks. Since it's an 8" duct fan, adding a section of ductwork to the fan intake would allow for reasonably accurate measurement of airflow, and the fan has a built in control for speed so hitting an approximate depressurization level should work.

    In no way am I thinking this will be an accurate measurement, but it should show clear trends and be easy enough to leave set up in a rough window opening that has yet to be cut out. If my rough measurements show 3 ACH50 I know I still have a pile of sealing to do!

    I would imagine the stability of a home made system like this will depend largely on how windy it is on a given day. On a calm day I could see getting very stable performance out of something like this. On a windy day I bet the airflow readings would be all over the place.

    Lance Peters

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