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  1. #1

    Return air for heated crawl space

    Hi folks,

    I'd really appreciate some help here. I recently bought and moved into a house with a 10'x10' heated crawl space under an addition to the house. As the weather turned, we had some mice move in and I located their entry point to the crawl space, which had easy access from the outside and the inside giving them somewhat of a red carpet into the house. Part of the problem was that whomever did the HVAC didn't use a collar for the ducting entry, so there was a wide open path for mice into the house. I suspect much of the work was done DIY, based on other things I've seen.

    I've completely sealed the crawl space, which leads me here for your help. The crawl space is heated via a duct from the furnace. However, there is no return air in the crawl space. Previously, there were enough cracks into the house and to the exterior to give the air somewhere to go. Now that I've sealed it, do I need to put in a cold air return as well? Or would a vent to the outside work?

    More information about the crawl space: 10'x10', floor is dirt, covered with poly vapor barrier and gravel. Walls are concrete and insulated with pink styrofoam. Rim joists are insulated with batt insulation and covered with poly vapor barrier. Ceiling (floor of addition) is uninsulated.

    I live in a cold climate, down to -25F in the winter.

    Thank you for your time!

  2. #2
    Join Date
    Jan 2005
    Location
    Emerald Coast
    Posts
    940
    .

    Are you in an area where radon is common?

    http://www.radongas.com/radon_map.htm
    ..
    Do not attempt vast projects with
    half vast experience and ideas.
    ...

  3. #3
    Quote Originally Posted by superheatsleuth View Post
    .

    Are you in an area where radon is common?

    http://www.radongas.com/radon_map.htm
    ..
    We're in an area that has reported exposures of 3-5 pCi/L, so I guess that puts us in high Zone 2 / low Zone 1 area.

  4. #4
    Join Date
    Apr 2012
    Location
    winnipeg
    Posts
    1,330
    well ....
    it was working.... played with it.... now its broke.... whats the going hourly rate for HVAC repair

  5. #5
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,583
    I would not put a return in a crawlspace.

  6. #6
    Join Date
    Sep 2007
    Location
    Boise, ID
    Posts
    4,332
    I would seal up the supply duct and add electric or gas heat to maintain crawl temperature just above freezing. Unless you have to deal with permafrost. Then it gets tricky, dealing with foundation and all.
    If a nation expects to be ignorant and free, in a state of civilization, it expects what will never be. (Thomas Jefferson 1816)

  7. #7
    Join Date
    Aug 2012
    Location
    North Dakota
    Posts
    518
    I'd have to agree no return as it would add to latent gain as well as possible smells and other airborn sh?t not sure you should get rid of supply I'd let it balloon

  8. #8
    Thanks for the replies! No return air it is then. I was worried about the smells and dusty gravel in there so I'm happy to hear it's not the recommended solution.

    Not sure about ballooning it, because the air has to go somewhere -- I wouldn't know if its finding cracks into the house, or to the outside.

    I'm thinking the solution could be a one way exhaust valve (e.g like for central vac, bathroom exhaust fan, etc) to the outside. That way I'm ballooning it and making sure the cold air's going outside. I'd like to consider that before electrical heating of the floor.

    Is this a stupid idea?

  9. #9
    Quote Originally Posted by mechanical'al View Post
    I'd have to agree no return as it would add to latent gain as well as possible smells and other airborn sh?t not sure you should get rid of supply I'd let it balloon
    What does "latent gain" mean?

  10. #10
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,551
    Quote Originally Posted by Yorkergizer View Post
    What does "latent gain" mean?
    Latent heat is heat required to change liquid to vapor or vapor to liquid without changing temperature. In other words its the energy used to remove the humidity from the air in an air conditioning application.

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