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Community and Q&A

Struggling with air leakage

bHqUcamKme | Posted in Energy Efficiency and Durability on

Again, I thank you all for your helpful input. You combined experience is making me better at my job everyday!

I am really struggling when it comes to recommendations for homeowners about air sealing. For example, I did a blower door test for a customer which came back at 1,550 CFM. The minimum ventilation requirement (using .35 ACH) comes out to around 1,600 meaning that they shouldn’t seal any air leaks without installing a mechanical ventilation system. Yet they had significant air intrusion around a fireplace insert, and air leakage around the knee walls on their second floor are causing ice dams.

I feel like I’m stuck telling everyone I talk to that they need to install a mechanical ventilation system when that just doesn’t sound feasible. What am I missing?

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  1. GBA Editor
    Martin Holladay | | #1

    Don't resist the program!

    A mechanical ventilation system can be as simple as a bath exhaust fan left on 24 hours a day. (Ideally, you'll install a low-sone 50-cfm or 80-cfm Panasonic fan.)

    Your customers will be much more comfortable, and save energy, if you seal up the air leaks and install a mechanical ventilation system.

  2. dickrussell | | #2

    To what Martin already said, I'll add more ammunition for you to shoot. Natural air leakage is undependable. At times it may be too much, costing you energy and draft discomfort, and at other times it may be woefully inadequate, making for a stuffy house that makes you want to open windows for fresh air. Worse, at all times it is largely uncontrollable, totally dependent on outside air conditions.

    Your gut feel is advising you correctly. Do the air sealing to eliminate excess uncontrollable leakage, and provide a means to ventilate adequately and under control.

  3. bHqUcamKme | | #3

    I assume that I should include the conditioned basement in my total volume calculations, correct?

  4. Katy_Hollbacher | | #4

    Curtis, to calculate typical ventilation requirements, rather than the .35 ACH approach I'd suggest using the ASHREA 62.2 method (which takes into account floor area and estimated occupancy rather than just volume; the latter can easily under or overestimate appropriate rates) or at least compare the 2 numbers & use your judgment from there. See page 1 of the attachment for a version of these calcs from California's Title 24 code, or try this online tool:

    Yes, you should include all conditioned living spaces in the volume or area calcs.

  5. sunstone | | #5

    The attachment seems damaged ,could you try that again?

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