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Air leaks discovered after blower door test

Norman Bunn | Posted in Energy Efficiency and Durability on

I was not present for my blower door test this past Friday, but am pleased to know it met Energy Star specs (which will get me a lower power bill rate).

However, that night I was working outside and saw light from the interior under two doors to the garage (unconditioned) from the mudroom (conditioned). The installation contractor had left the seals off the bottoms!

Not wanting to pay for another door test, I am wondering how much impact two 3′ x .5″ slots (0.25 cu ft) will have on my results.  IOW, how much air will pass thru such holes every minute at 50 pascals?

Norman
CZ 3A

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Norman,
    There are too many variables to provide an answer. For example, the answer depends in part on the size of your house.

    But I don't think the answer is very relevant. Just adjust the weatherstripping or the adjustable sills, and be glad that you noticed the leaks.

  2. Norman Bunn | | #2

    40,400 cu ft per the tester.

    I want to know if these leaks are making a significant difference in the total or should I spend the effort to find more. If it is just a percent or so, then probably not, but if an order of magnitude more, then probably.

  3. Jon R | | #3

    You can calculate the effective leakage area figure and then compare your leak area (36 sq inches) to this.

    http://www.residentialenergydynamics.com/REDCalcFree/Tools/AirLeakageMetrics.aspx

  4. Bill Dietze | | #4

    Norman, Joe Lstiburek gives a formula for this in his builder's guide to cold climates for air flow through a hole (through a "squared edged orific"). That formula is cfm = 1.07 x A x (P)^0.5, where A is the area of the hole in sq.in. and P is the pressure difference in Pascals. For a 50 pascal blower door test and your hole, the air leaking under your door is 1.07 x 36 x 7.07 = 272 cfm. Elsewhere in his book, Joe equates a 1 sq.ft. hole with CFM50 = 1000. Thus the 0.25 sq.ft. hole under your doors added 250 cfm to your blower door result.

    Bill

  5. Trevor Lambert | | #5

    What are your actual numbers, to put this in context? Energy Star air sealing specs are a joke. The most recent spec I could find was 3-5 ACH50, from 2012. Any new build house that wasn't built by a blind man would likely meet that spec. They might have tightened up a bit since then, but probably not by much, since their target is only to be 20% more efficient than a minimum code built house. Just the air leaking through the bottoms of those two doors is about three times as much as my entire house.

    I am kind of confused when trying to reconcile your original comment with your reply #2. The air flow through the missing seals has no bearing on unknown leaks. Obviously you should fix the missing seals, and if you were happy with the numbers before then you'll be more happy afterwards.

  6. Norman Bunn | | #6

    The number is 3.6 ACH50, which beats the Energy Star 5 ACH50. I was planning on something below 3, preferably 2, so I will be looking for more leaks. I know the attic access doors need more attention. My plan is to seal a door with 6 mil plastic, use a floor fan like they use to dry wet areas to depressurize the space and use a Wizard Stick to ferret out the culprits.

    The house should be tighter than 3.6, based on all the work I have done to seal things, so I suspect there are some hidden leaks that are not so obvious from visual inspections.

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