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Air sealing did not improve blower door test results. Why?

halaby | Posted in Energy Efficiency and Durability on

I recently air sealed and insulated my house as follows:

1) air sealed 40 recessed cans;
2) air sealed all major attic penetrations;
3) spray foamed all my basement and crawlspace sills;
4) topped up all the attic insulation to 50R

The blower door test results were the same on post-test and pre-test. How does that happen?

Alternative retest methods did not change this outcome — no improvement detected. The energy auditor could not explain it.

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  1. GBA Editor
    Martin Holladay | | #1

    Here are some possible explanations:

    1. The blower door tests weren't performed correctly, and their results are inaccurate.

    2. Your air-sealing efforts were sloppy.

    3. Your air-sealing efforts were excellent, but there is a monstrous hole in your thermal envelope that you have not yet located.

  2. user-1115477 | | #2


    First, your # 4 doesn't necessarily help with air sealing.
    Also, similar to what Martin said with his #3: It sounds like your leakage is in places different from those you sealed. As surely you know, there are many other places for infiltration than those you mentioned.

  3. davidmeiland | | #3

    There is no substitute for blower door-guided air sealing. You run the fan the whole time, either pressurizing or depressurizing, find the leaks, seal them, and confirm as you go that the manometer shows a reduction. I have done pre and posts tests for crews that did not do this, and they often don't get much improvement. For that matter, I don't do much without the fan running myself.

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