How to safely install dehumidifier through floor joist?

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Posted by: from Moose Jaw
9/20/2015 at 12:18:58 PM

I'm trying to install a Humidex dehumidifier in my basement. The location that works best to mount it would require me to drill through a floor joist, but the vent requires a 6 inch opening. Is there anything I can do to a 2 x 10 floor joist so the structural integrity is not lost?

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Date/Time9/21/2015 at 8:15:21 AM

Hi Curtis,

So the general rule for floor joist holes is that you cannot be closer than 2 inches from the very top or very bottom, although larger holes should be completely centered in the joist. The size of the hole cannot exceed 1/3 of the size of the joist. So for a 10" joist, the hole should not exceed 3.33" in diameter, or realistically a 3-1/2" pipe. Is there not a way for it to be installed and create a bulkhead?

Good luck, possibly posting some pictures will help you in ideas to complete it properly.


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Date/Time9/21/2015 at 10:50:18 PM

Hi Curtis,

Alex nailed it. No more than 1/3 of the joist width and centered. In your case that would be 3+ inches so not doable. The only way you could do it would be to run the 6" pipe in the joist cavity to an end wall and then drop and turn it to go out the wall you want it to. You would then build a bulkhead to hide the pipe.

Good luck with it.

Jim Kuzma

Kettleby Handyman

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Curtis in Moose Jaw
Date/Time9/22/2015 at 12:12:39 AM

Thanks for the replies. I was pretty sure that's the answer I was going to get. My problem is my joists run East-West and I wanted to put it on the North wall and whoever finished the basement built the basement walls about 2 1/2 to 3 inches away from the concrete which cuts down on the room between the outer board (ledger?) and the first joist. I guess I'll have to come up with a different location.

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