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Converting crawlspace to a conditioned room - transfer grills a fire hazard?

Post in 'DIY and General non-hearth advice' started by rmcfall, Oct 14, 2007.

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  1. rmcfall

    rmcfall Feeling the Heat

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    I have decided to convert my crawlspace into a conditioned room. An article from the Building Sciences website shows different methods as far as supplying conditioned air and recirculating it, but I was wondering what people here think.

    I have an almost full basement, with the exception of one part that is a crawlspace. The crawlspace is in a corner, so the finished part of the basement shares two block walls with the crawlspace. One of these shared walls contains a return air at floor level that leads to the air handler, which is in the crawlspace.

    Since my air handler is in the crawlspace, it is easy enough for me to cut a register into the plenum to supply conditioned air to the crawlspace. My question is what to do about circulating the air? One method I read about in one of the Building Sciences articles was to use passive transfer grills. They showed transfer grills being placed in the floors of the rooms above. From reading posts on this website, however, I thought it was a fire hazard to have open grills? In my case, I thought it would make the most sense to place a passive transfer grill in the shared basement wall at ceiling level above the return air grill. This way, the air would be passively drawn from the crawlspace through the shared basement block wall with the return. Or would it be better to place the passive transfer grill in the other shared wall, so that the transfer grill is as far as possible from the basement return air? Does this make sense to do, and is it OK in that the transfer grill in the block wall would have no ductwork attached to it? Elk?

    And as far as the foam board used to insulate the crawlspace walls, have people here used fire-rated foam board when doing this since it isn't covered with drywall?

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  2. rmcfall

    rmcfall Feeling the Heat

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    Any thoughts? Anyone?
  3. Gooserider

    Gooserider Mod Emeritus

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    Not sure on the air handler, I know that Elk says you are supposed to have a return and a supply in each room, but not sure what that entails. However I would be leery about cutting holes in the air handler w/o some pro advice, I'd be worried about either getting to much air into the room, or upsetting the balance of the rest of the house.

    As to the foam, I don't think there is any that can be used in a "habitable space" and left exposed - it needs to be covered w/ something, either drywall or 1/4" + thickness of panelling / plywood / osb, etc.


    Gooserider (not an expert on this, trying to answer because nobody else did...)
  4. rmcfall

    rmcfall Feeling the Heat

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    Thanks for the reply. My HVAC is new and I checked with the installer about cutting out a spot in the plenum for a supply grill to get conditioned air into the crawl. He didn't seem to think there was a need to put in any transfer grilles due to leakage, but I thought I'd ask to see what others think.

    Re supplies and returns--I don't have returns in every room. I've got a large return in my main hallway that leads to bedrooms, a large return off the master bedroom, as well as one in my open kitchen/family/dining area, and one in my basement. Seems to do the trick without any problems. I have a Carrier Infinity system, which is sure to tell you if there are any issues with air flow, static pressure, etc.

    I understand that foam board has to be covered in habitable spaces. Even though a crawl space isn't habitable, I wonder whether coverage is needed there as well to serve as a fire barrier...

    Thanks again for responding.


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