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Bathroom fan exhaust

I just put in a new bathroom exhaust fan that I will be exhausting to the exterior wall. The pipe is 6". I have 8" exposed siding but the only size I am able to find for the exhaust cover is 9". How do you handle the overlap in siding or is that not of a concern?

A. Spruce
Re: Bathroom fan exhaust

If possible, I would try to tuck the top of the exhaust cover below the bottom edge of the siding so that it sits fully on one piece. This would allow caulking of the most important top and side areas. The bottom can also be caulked or install a small shim to fill the gap and then caulk both the shim to the wall and the cover to the shim.

If you can't do the install like that, then install however, then either use foam caulk backer or cut a wood shim and caulk everything to seal against critters and water intrusion.

Re: Bathroom fan exhaust

You would cut out a portion of the siding, say 10 or more inches square, and install a plaque of wood, thicker than the thickness of the two laps of siding, and cut your duct-port into that. Ideally, if very exposed, you would add head-flashing at the top so water couldn't enter, and a small rabbet at the bottom overlapping the siding 1/2" or so would complete the water-detailing, after you caulked the edges.

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