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Corganer 11-06-2013 08:29 PM

Seal Inside of Bath Fan Housing?
Hello All! I just installed a new bathroom fan. Everything is connected well and the fan is working. 4" duct work, 110cfm fan. Anyway, It does actually suck air up but I noticed air is shooting back down through gaps inside of the fan housing (NOT outside). My question is ... would it be ok to caulk gaps inside of the exhaust fan housing? It seems like it would be ok, but then I started thinking about what if it is too much air for the 4" duct work and the air is simply pushing back out?

I have seen a couple of people online say to fill in gaps with caulk but most of the things i have found only deal with sealing outside of the housing dealing with drywall gaps.


nealtw 11-07-2013 06:19 AM

If the pipe is too long or has restrictions that limit the air flow , sealing it will only make it more noisy. If air can't move fast enough the fan will make a chopping noise and people think they have a noisy fan. If you make the duct bigger to take more air you have to insulate it because slower air can cool and moisture can condense in the duct and drip back thru the fan.

CallMeVilla 11-07-2013 07:54 AM

Neal is right ... While 4" was the standard for many years, higher capacity 6" fans are the best. I have literally seen showers where moisture gathered and peeled the paint -- despite a 4" fan running.

You can get foam "rope" to test seal the perimeter of the fan housing. Painters call it "backer rod" and use it to backfill large cracks before caulking. It is cheap and you can pack it into the gaps to see how it impacts the fan noise. If your fan gets loud, just pull the rope and go to Plan B = larger ducting.

Corganer 11-07-2013 08:03 AM

Thank you both! I definitely hope the foam rope works because this is a condo unit so it would be a few dollars vs. thousands the way the building is set up.

Corganer 11-07-2013 10:36 AM

Update: I sealed INSIDE housing unit and the fan did not get louder. That's good. Now I am not done with my exhaust fan project and still need to fill drywall gap on one side of the fan. It is about 1.5 inch gap. It seems like the fan is sucking air from the drywall gap. It is only happening on that side (of course?). Does that sound right? Fan is on ....sucking air from gap right next to fan (into crawl space). Meaning, once I close that drywall gap like I am supposed to anyway ...maybe the air intake will pull from where I need it to?

CallMeVilla 11-07-2013 01:14 PM

Again, you can use inexpensive foam to insulate that gap. This time, you can buy the insulating foam tube that is used for hot water pipes. Get a small diameter for 1/2" pipes. Cuts easily with a razor knife. You can take a wedge out of it to turn a corner.

Should fill in that big gap nicely.

Also, you can get serious with silver aluminum tape (no, not duct tape). This tape is extremely adhesive, bright silver metal foil. You peel off the backing and it will permanently adhere to metal or even painted drywall. So, install the backer rod and/or foam tubing. Cover with silver tape. tape

Done! :D

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