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Old 09-26-2011, 08:45 PM   #1
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Venting a first floor bathroom fan

I had this post in HVAC for theee days. Got 89 views, but no response so I decided to repost it here.

Venting a first floor bathroom fanWhen our house was built no bathroom fans were installed. Now, I have a few questions before beginning this project.

1. I can run the duct work between the ceiling joists between the first and second floors and vent it to the outside, but will have to cut through the sill plate? to do this. Will this be a problem? Structural concerns, etc. Tough making duct work connections, too as, once the existing fixture is removed, I will have to reach in over the shower unit to drill the hole, make the connections, etc. But my main concern is whether it's ok to make this cut.

2. Except for one joist, I could go the other way. Now I know I shouldn't cut a 4 inch hole in any joist, but I was thinking about moving the light fixture (which will be replaced with a light/fan unit) over so that it is on the other side of the joist. Then, of course, I will still have to cut a 4 inch hole to the exterior through the sill plate which is running parallel with the joists. This would make connections, etc much easier since it will be a very short run less than 2 feet. Structurally, is this unwise or is the the same as making the cut in the sill plate (don't know if that's the right name) which is perpendicular to the floor joists.

Thanks in advance for any help you can give me with this


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Old 09-27-2011, 03:44 AM   #2
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If you are referring to the top plate I would not cut it. On the other hand, if you are referring to the rim joist, you should be able to.

I would go with the second option, as the shorter run is going to give you the best ventilation.


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Old 09-28-2011, 01:47 AM   #3
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I get the impression that what your calling the sill plate is actually the rim joist as 191one mentioned.

I'm not sure I quite understand option 2...unless your floor joists are 24 OC (On Center...which means they are 24" apart). Most floor joists are 16" or 12" OC.

Does that bathroom have a window to the outside? If so, that is why there is no vent.

If you can do option 2 without cutting a floor joist...that is the way to go....drywall is easy to work with...
Even if you are on the right track, you will still get run over if you just sit there.

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bathroom fan venting

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