enter image description hereSo I have two basement rooms about 500 sqft each and I want to balance the humidity between both rooms. One room has a dehumidifier and drain so I'd like to cut a transfer grille between the two rooms so the dehumidifier can work through both rooms.

How big of a transfer grille should I have between the two rooms for the dehumidifier to be effective across both rooms. How far above the floor should the grille be mounted?

Looking at the original blueprints - it looks like they had planned to put 24x14 transfer grilles into the wall - but the actual building does not.

  • Presumably the speed at which it needs to occur has some impact on the size of grill ... As does the rate of ingress of water that is causing the humidity..
    – Mr R
    Apr 27, 2021 at 22:46
  • it doesn't have to happen fast - to keep the basement from getting mildewy - not very much water so let's say a humid summer day dehumidifier over the course of 8 hours - 70% -> 50%... Apr 27, 2021 at 22:57
  • 500sqft is quite a big space - I imagine the shape of the room will mean that without some mechanical air movement the damper areas might still stay damper (even if the room is as a whole relatively dry).
    – Mr R
    Apr 27, 2021 at 23:02
  • Is there any moisture generated in the other room other than from the concrete (bathroom, laundry?)
    – Ed Beal
    Apr 27, 2021 at 23:33
  • no - just a drain ... and occasional laundry but that's not very often. It's two rectangular rooms side by side - I've updated with blueprints and noted that original plans seemingly had 24x14 transfer grilles in the plan... which were not built Apr 27, 2021 at 23:49

1 Answer 1


Since the original plans seem to call for a 14x24 grill, that seems to be a really good place to start.

I'd plan ahead to either add a fan to encourage air movement if that's not sufficient and/or add more venting between the rooms.

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