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Conditioned or unconditioned crawl with mini-splits

DG Builder | Posted in Green Building Techniques on

I am looking at putting a mini-split into a new home but can not seem to find an answer on how or if I should condition my crawlspace. I know crawls aren’t the best route but I don’t have the extra $17k to do a basement and a slab isn’t an option. So can I build the crawl as a conditioned space without the hvac runs keeping it climate controlled or how should I go about this? I’m willing to put another head in the crawl if that’s what needs to be done to make it work.

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  1. JC72 | | #1

    Everything I've read about condition crawlspaces includes: #1 Supply duct in the crawlspace, #2 Transfer grills between the first floor and the crawlspace.

    What's preventing a slab? Is there anything going in the crawl space?

    One other option is to leave the slab unconditioned and insulate the underside of the first floor (fluffy stuff, then close it up with rigid foam on the underside of the joists.

    My two cents.

  2. GBA Editor
    Martin Holladay | | #2

    DG Builder,
    Of the two methods used to help keep crawl spaces conditioned, the one that makes the most sense for a house equipped with ductless minisplits is to install a properly sized exhaust fan in the crawl space (usually in the rim joist area, blowing out), and a transfer grille in the floor of the story above (that is, in the crawl space ceiling).

    Building codes require one of two methods to be employed to keep the moisture under control in a crawl space; the method described above is one of the two methods. Full details can be found in this article: Building an Unvented Crawl Space.

    Note that if you get the details right when you build your home, your crawl space may stay dry without conditioning. That means that after 6 months, you may be able to turn off the exhaust fan. Of course, you should monitor the humidity down there if you take this approach.

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