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We are building a new garage with apt above and storage room at the back in Houston TX. It's replacing a small garage with back storage room which was very poorly constructed and had major moisture issues.

Trying to figure the best way to keep the new storage room dry. Initially thought of using a humidity sensing exhaust vent on the exterior wall but then realized it would just end up sucking in outside makeup air which might be even more humid than the exhausted air.

Can think of three possible solutions but looking for guidance/opinions.

  1. Use a dehumidifier. Possible cons:

    • Would have to drain thru the wall since we would not be in the room every day.
    • Might not work during the couple of months that temps are in the 30-40s.
    • Takes up storage space.
  2. Use thru wall AC unit. Possible cons:

    • More expensive.
    • Cooling vacant room.
    • Still have trouble during cooler months.
  3. Run a AC duct down thru bedroom closet and thru garage ceiling to storage room.

    • Long duct run just for storage.
    • Additional cost and possible issues with general contractor due to changing plans.
    • Would need it's own return also wouldn't it?

Any other solutions? Is this even necessary? We're a bit paranoid as the previous storage had {and our house as well actually has} moisture issues.

We could just do nothing and see what the RH level is but then we'd be responsible for the whole install cost. If we decide before I can probably get at least some of it covered in the original construction contract.

Thanks!

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I think a small dehumidifier in the storage room would be the best choice. If the temp is two low for a dehumidifier to work I would think maybe putting DriZair pots like the link shows would work. We use Drizair in our motor home when we are not using it and we only have problems if we forget to put the crystals in every month or so.

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A typical dehumidifier and air conditioner are fundamentally the same thing. They use vapor compression refrigeration to move heat from one heat exchanger to another. Both have a cold side, which cools air that flows across it, causing condensation; the difference is that the air conditioner's hot side is outside the space, cooling it, while the dehumdifier just heats back up the air it just cooled (effectively warming the space). Relative humidity is dependent on not just the amount of moisture in the air, but also the temperature; the cooling effect of an air conditioner works against your goal of reducing relative humidity while the heating effect of a dehumidifier works towards it. So when your goal is only to reduce humidity, a dehumidifier is superior to an air conditioner.

Running ductwork shared with your interior to a garage space is not safe and is generally not legal. You should not do it.

In the winter, if humidity is still high enough to be a problem, you can use a dessicant, or you can simply heat the space.

A sheltered, ground coupled space like some garages can be substantially cooler than the outdoor temperature; in a humid climate, this means very high humidity is inevitable. You will likely need some dehumidification; the quality of the construction will just affect how much of it you need.

  • Zhentar, I should have been more precise in my description. The storage room is on the ground floor behind the garage, however it is a completely separate space. The storage room is on the same slab but it's floor is about 4" higher than the garage, there is a finished wall between them and the storage room only has one opening, an exterior door. The AC duct would run from the attic down through a closet in the 2nd fl apt and then through the floor joists to the storage room ceiling. Given that info would it still be better to just use the humidifier or the supply and return AC ducts? – Niwashikun May 21 '16 at 22:51
  • Yes; even with your house AC, you have the same basic downside; the cooling is counterproductive. It would be cheaper to run than a window unit, but it would likely not be cheaper nor more effective than a dehumidifier. – Zhentar May 23 '16 at 15:20

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