GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Does the Ultra Aire whole house dehumidifier cause concerns in a foam attic?

suect | Posted in General Questions on

Looking into the Ultra Aire dehumidifier for our foam insulated home.  Any thoughts if it would impact the attic due to temperature changes?


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. jameshowison | | #1

    UltraAire makes two kinds, a single box or a split system. The single box ones (e.g., 98H) do blow out hot air when dehumidifying (ie they convert latent heat to sensible heat). The split system (e.g., SD12 pushes it's heat outside.

    Not quite sure why foam insulation would matter, perhaps you are seeing elevated humidity levels in your attic?

    1. Deleted | | #2


    2. suect | | #3

      We purchased this unit to maintain the humidity on the main level as well as the foamed attic.

      The humidity in the attic increases with temperature increases and is the reason for this question. Should the split system be used in a Texas attic?

      We use the AprilAire ventilation system. Could this be a big part of the problem? I try to keep the humidity between 43- 50% with the a/c and fresh air.

  2. jameshowison | | #4

    Well, I'm no real expert, but the operation of the dehu should increase temperate but decrease water in the air. Since relative humidity drops as temp rises (even with the same amount of water in the air), the dehu operating correctly can't cause both to rise. So extra water must be coming from somewhere.

    Not sure if the unit also has ventilation with outside air; might it be that it does and that it is also pulling in outside air. Assuming that air has plenty of moisture in it (which it will in Texas this time of year) that could cause a rise in relative humidity. Check that the control for the vent is set to "Auto" (and that there is a backdraft damper in the outside air duct?) and that vent is set to 10-50 (ie 10 minutes open in each hour) or similar.

    Or you should check that the drain on the dehu is draining properly. Might need to be cleaned out with compressed air? If the water isn't making it outside then operating the dehu would cause temp to rise (but water would stay the same; hmmm, so relative humidity would decrease).

    Try not running the dehu for a while and see what happens? You might need a good sensor for both temp and humidity, like the ones:

    If, with the dehu off, the relative humidity rises (with temp stable) (or dewpoint rises) then the water is coming from elsewhere (and rising to the attic). In that case tackling water sources elsewhere matters (and the dehu is helping).

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |