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Old 12-04-2010, 10:00 PM   #1
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Venting bath fan

I'm going to try installing a bath fan in my 1950s building, right now there isn't one. I was hoping to be able to vent straight out the side between the joists, but there are some cross braces in the way and I'd have to go through both concrete block and (old school) stucco.

If I go straight up, I'll have to have an almost immediate elbow which the directions say not to do. The total vent run is going to be only about 18", since it's a flat roof. Seems to me that it will still be fine, but maybe not? If I do that, should I put in 2 x 45 degree elbows instead of 1 x 90? I have about four feet that is clear of bracing, but of course the fan accounts for some of that.

Would be nice to have some idea before I put it in completely wrong.

Also, do I have to use metal vent or can I use PVC?



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Old 12-05-2010, 01:01 AM   #2
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no bends? check on a panasonic whisper green. an elbow should be no problem, and they (at least some) will adjust themselves to make sure they are putting out what they are designed to do under different installation configurations. they are very quiet and somewhat programmable. whatever you do, seal the vent pipes impeccably. i don't think the type of pipe matters to the fan, but the "normal" stuff is cheap and easy to wiggle around stuff. i ran mine into the abs out the roof; what can it hurt? seal, seal, seal.


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Old 12-05-2010, 09:09 AM   #3
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Just take out the cross bracing. I'm pretty sure the joists have stabilized by now. You can always pop in a 2x4 at the bottom, laying flat.
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Old 12-05-2010, 09:09 AM   #4
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Key wording here: Flat roof. Unless you have experience with dealing with flat roofs, placing any protrusions up through them and sealing this--maybe not a good idea there either. Use the metal piping. Trying to fit PVC while up in the attic is not a good thing. As stated, fit it properly, and seal properly. Using two 45's instead of one 90 will always give better flow properties--IF you have the room to do so. It doesn't sound as if either direction is going to be easy.
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