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Thread: Crawl space encapsulation; foundation vent fan and radon mitigation

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    Crawl space encapsulation; foundation vent fan and radon mitigation

    Ive read that the EPA guidelines are that a foundation vent fan be installed when the craw space is encapsulated. That is because the soil gases will have nowhere to go to. Id say that this makes sense but my question would be if this is still necessary if a radon mitigation system is already installed and pulling air out right from under the vapor barrier installed in the crawl space?

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    R600a's Avatar
    R600a is offline Professional Member*/Membership Committee
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    Personally I think a crawlspace dehumidifier set up for ventilation would be much more effective and also prevent issues with moisture and biological growth.
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    I’m not clear on why an encapsulated crawlspace should have a vent. Doesn’t that defeat the purpose of encapsulation? I agree that a radon system should accomplish the venting.
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    The way I read it was that the fan will exhaust air from the encapsulated crawl space and will not allow air in. That is to remove the gasses that might still get into the crawl space and then eventually in the house if no exhaust vent is present.

    Anyway I found the original EPA doc https://www.epa.gov/sites/default/fi...icy_record.pdf. See section 1.4, but also look at the 1.4 revision. And it looks like I just found my answer to my original question:

    Provide conditioned air at a rate not less than 1 cfm per 50 sq. ft. of horizontal floor area. This can be achieved by a dedicated supply (2009 IRC section R408.3.2.2) or through crawl-space exhaust (2009 IRC section R408.3.2.1). However, if radon-resistant features are required (see Specification 2.1), do not use the crawlspace exhaust method.

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    You cant exhaust what cant be made up!

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    The negative pressure exhaust under the vapor barrier is effective in most cases. But this does not deal with make-up fresh air to the home including the crawlspace. The home has make-up air requirements for the clothes drier, kitchen hood, and bath fans. Also most suggest a fresh filtered air change in 3-4 hours to purge indoor pollutants and renew oxygen. If the home is located in a green grass climate, the a/c needs to be set up to deal with moisture in the make-up air and from the occupants to maintain <50%RH though out the day when the there is enough sensible cooling to remove the latent moisture. Evenings and rainy days when the outdoor dew points are +55^F. A dehumidifier like the Santa Fe Ultra/Broan/Trane with the fresh filtered air option are designed to be provide fresh filtered air,(merv 13) and maintain <50%RH through out the home by connecting to outside air and the ducted a/c.

    Keep us posted on what you do and how it works.

    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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