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  1. #1
    Join Date
    Apr 2003
    Location
    St. Louis
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    blower door test

    I'm getting a blower door test of my house in southern Missouri by the electric coop. like to know what is good reading and bad readings are. Then is their a formula to take their reading and cubic feet of area of the house and find out how many cfm it will take to over come the infiltration. windows, doors. siding with tyvek and two multi split vrf systems both two ton, six wall units for 1900 sq. ft. cooled the house this hot summer with only one system but still have a high humidity 59% to 65%.this house has almost no drywall, pine lap siding and crawl space with 6 mill plastic.

  2. #2
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
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    479
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    The answer to your questions are best answered on line. I researched that a few years ago because I was thinking about adding that service to my TAB company. I didn't add it because I do not agree with some of the methods. The tests are run at 75 Pascals which is 0.30 inches of water. That kind of pressure does not even exist in commercial buildings and creates leaks that otherwise do not exist. It is a good test for finding infiltration just apply common sense.

  3. #3
    Join Date
    Mar 2017
    Posts
    12
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    yeah, look for the HERS rating scores......you will see a lot of the air changes per hour.....if its really tight and humidity is an issue, you may need an ERV

  4. #4
    Join Date
    Mar 2017
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    I should have added youtube has some people explaining it ....and calculate the CFM to air changes

  5. #5
    Join Date
    Mar 2017
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    12
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    I would post the links, but I need a couple more posts

  6. #6
    Join Date
    Aug 2004
    Location
    S.E. Pa
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    7,140
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  7. #7
    Join Date
    Nov 2000
    Location
    Indiana
    Posts
    328
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    I know the original post was from last October, but for anyone else having a blower door test done...

    About everyone doing residential blower door testing is doing a "one-point" test. The test results are going to be in CFM@50 pa. This can give you a relative idea of how tight your building is but there are some caveats. Calculations done using the CFM@50 number assume that the leakage is relatively evenly spread around the building - high and low. So it you were trying to determine estimated natural infiltration for load calc or IAQ purposes, the location of the holes makes a difference. If all the holes high in the building were sealed, the actual ACH could be substantially lower than you think. But still, it is really the only good place we have to start.

    Also, a well-used formula to determine ACH is CFM@50 / N-factor x 60 / volume. The variable here is the N-factor - determined by things like climate, wind, shielding, leak type. In Indiana, we have used between 16 and 23 for quite a few years but I believe new data is suggesting that our buildings are not as leaky as we assumed and the N-factors could be substantially larger. Like Hearthman said, the TEC manual has great info - Appendices E / F discuss this.

    I think one of the best things about a blower door is that it kind of "normalizes" leakage in that it gives us numbers to help us determine if there are air-sealing opportunities that exist in a building. You get a feel for what is high and low and where the air-sealing opportunities lie. I do think that ACH@50 is better at this than trying to determine ACH nat. Don't have to bother with the N-factor (I believe Chapter 6 in the TEC manual). High performance housing uses this and I think it is better for rating a home. My house, for example, is about 350 CFM@50. Trying to calculate ACH nat would be tough because my house does not leak high - air can't come in if it can't go out from a stack effect perspective. 350 CFM@50 works out to about a 1.3 ACH@50 - pretty tight. I just think this normalizes a comparative look at different buildings a bit better.

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