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Blower door test

user-1129453 | Posted in General Questions on

I am new to the field. I just took my brand new blower door out of the box and ran my first test though tectite software. My official training is at the end of the month sooo until then I need some help interpreting the results. From what I understand my house “scored” fairly well. 550 on ring B for the depressurization and 650 on the pressurization. The results sheet also showed 18.6 CFM and .14 ACH on depress. and 20.9 CFM and .16 ACH on pressure. I did not close off any exhaust fans, return registers because nothing that I have seen/read said anything about that. The house has a crawl space and attic.
My questions are:
What can I interpret from the scores if I tested on a 1000sqft house? How much does sqftage matter? Do I need to seal exhaust fans to the outside when running the test? Any good research website for novice?


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  1. GBA Editor
    Martin Holladay | | #1

    If you haven't seen it yet, you might want to read Blower Door Basics.

  2. user-1129453 | | #2

    Thanks for the link. I had read that article before but I read it more carefully this time. I think that is probably were my sqftage question came from. In the "is my house tight section" it mentions taking sqftage into account. I wasn't sure how much it mattered. Since I now know the formula for ACH, I think that maybe my volume calculation may have been off. My score of .14 is to good to be true.

  3. davidmeiland | | #3

    Sounds like you read the instructions that came with the unit and set it up for the test as they tell you. You get bonus points if you didn't have to crawl through the fan hole to place your green hose.

    One thing that's critical... the ring on the fan and the setting in the software (or on the DG700 if running manually) MUST match at all times. If they don't, you get a hugely inaccurate result. Get in the habit of double-checking this at least a couple of times during each test.

    IMO there isn't that much point in doing a pressurization test. You will be blowing a bunch of air out through the range hood and bath fans. The only time I do it is when doing blower door-guided air sealing. When depressurizing, you are pulling all the dampers shut, at least in theory... you'll be surprised at how much they leak air in.

    To get a comprehensive test, you need to put accurate data into TecTite. Measure the square footage of the house, then determine ceiling height(s) and calculate cubic volume. Get accurate measurements of indoor and outdoor temperature before the test and input those. Select a climate location from the drop-down menu and tweak the HDD and CDD data if appropriate. There is a data-gathering process that precedes every test.

    TecTite uses the climate info, wind exposure info, and occupancy info that you enter to estimate air changes under natural conditions. Sounds like your 18.6 and 20.9 are those estimates. You need to understand the formulas they are using to get those, and what factors contribute.

    You generally don't seal anything prior to a blower door test, unless there are temporary holes that will be sealed later. Example, if you test a house with a woodstove chimney but no stove installed yet, tape the flue pipe shut and make a note of it in your TecTite notes page. You don't seal heating registers, fan grilles, hoods, or much of anything. You may encounter passive air inlets in some houses and you need to know what to do about them, it varies by application. You need to learn about the hazards of fireplace ash, asbestos, dry plumbing traps, and more.

    Having a blower door is just the start. Learning to find leaks and fix them is the goal, unless you are just getting numbers for new construction compliance.

    Re your 1000 square foot house, at 550 CFM50, assuming 8 foot ceilings, you are at 4.12 ACH50. Reasonably good result, assuming all the test settings were correct.

    Hopefully, your class will cover how you should handle all of this, to comply with whatever programs or codes you are dealing with.

  4. user-1129453 | | #4

    I did get those extra points! but I also got some funny looks from the neighbors. :) I am looking forward very much to the class. I am starting with only compliance as a HERS rater then building my business up as auditor. That makes a lot of since about the pressure testing. Even though I scored well, sealing is in my homes future.

  5. davidmeiland | | #5

    I would offer some of the funny-looking neighbors a free blower door test. That's about the best way to get good at it, and experience some of the issues that will come up. You can practice your leak-finding detective skills and you never know, you might sell some air sealing work that way too. Besides that, read the Energy Conservatory manual cover to cover and try to absorb all of the details--there is a wealth of info in there.

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