Using "Damp Rid" chemical dehumidifier in a small room

Discussion in 'Remodel Forum & Blog' started by Theodore, Sep 29, 2020.

  1. Theodore

    Theodore Member

    Joined:
    Sep 18, 2015
    Location:
    New York
    I have a small (5ft x 5ft x 5ft) "cold room" vault accessed from my basement. It's outside the envelope of the house (under 6" of dirt above too) except for the door from the basement. It's where the well pump and pressure tank is for my house. There is no vent or airflow in the room. Even though, years ago, I excavated the outside and exposed the concrete walls to apply tar and heavy plastic to waterproof, it still gets humid in there. 60+% RH is not uncommon according to hygrometer I have in there. But it also gets cold (40+/- in winter), which is why I do not want to leave the door open and/or vent it into my *finished* basement.

    I tried using my dehumidifier in there, but it frosts up pretty quickly and doesn't seem effective. Not to mention, I don't want to hear the thing growl if I can help it. I was thinking of buying a chemical dehumidifier like "Damp Rid", or making my own from calcium chloride (which is what Damp Rid uses). But I also read that calcium chloride is very corrosive and possible that any dust it creates can make rust an issue in that enclosed room.

    Has anyone used one of these chemical dehumidifiers to keep dampness down in a small room and are they effective for what I have in mind? I don't mind having to check and replace every couple of months.
    Any issues with corrosion?

    Thank you.
    Theodore
     
  2. breplum

    breplum Member

    Joined:
    Oct 2, 2004
    Occupation:
    Plumbing and heating contractor
    Location:
    San Francisco Bay Area
    I've seen them around. It won't do much with constant humidity IMHO.
     
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  4. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Unless you want the room to be cold, installing R13 rigid polyisocyanurate insulation (2", if foil faced) on the walls and R25 (4") on the ceiling of the exterior walls, and leaving the common wall to the basement uninsulated will raise the temperature in the vault to something near the basement temperature, which automatically lowers the relative humidity, and keeps the temperature high enough for the dehumidifier to operate without frosting up.

    The foam can be mounted to poured concrete or concrete block with foam board construction adhesive (formulated with solvents that don't attack the foam).

    If there isn't enough room to work within that space, insulating it from the exterior side with 2.5-3" of EPS (not polyiso, not XPS) on the sides down to a depth of 2' (in US climate zone 4 & 5 parts of NY, the counties in yellow or green below ) or 4' (zone 6, blue), with 5-6" of EPS above would achieve roughly the same results.

    [​IMG]
     
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