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Old 10-20-2010, 10:31 PM   #1
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bathroom exhaust venting


i have two bathrooms located one on top of the other. I need to vent both of them. I was thinking running the vent duct for downstairs through a chase and attach with the upstairs duct with a tee or wye, and then continue up to the roof. Is it allowed to share an exhaust port between two bathrooms this way? Would the portion that runs from tee to roof have to be sized larger or is 4" adequate? Is flex ducts ok to use here?

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Old 10-21-2010, 01:46 AM   #2
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bathroom exhaust venting


can't speak for code, but in my research on venting to the exterior, i have found several products that are designed to use one fan to vent multiple spaces. generally speaking, the larger duct you can use, the better (6" is better than 4"). also, stay away from the flexible stuff if you can.

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Old 10-21-2010, 02:04 AM   #3
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bathroom exhaust venting


my concern with venting multiple bathrooms is if using a regular ceiling mounted fans, one fan can push air into the other room.

Possible solutions:
1. Can be partially solved with a proper wye connection in the correct direction, but not 100% fool proof.
2. So other option is remote fan mounted after the tee or wye that pulls air from both bathrooms (that's probably the type of fan you're talking about), but that will wasting conditioned air when pulling from the bathroom that doesn't actually need venting.
3. So to solve that, I would use a damper system to only open the damper for the bathroom that needs venting, but now the system is needlessly complex. Of course, that's assuming code even allows for such a system.

edit: light bulb! another idea. Could you use a backdraft damper with separate fans, thus preventing air from one bathroom from venting into another.

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Old 10-21-2010, 08:19 AM   #4
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bathroom exhaust venting


The fans have a backdraft preventer. It comes with every fan. It's attached to the fan unit. You would attach the ductwork to the backdraft piece.
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Old 10-21-2010, 10:28 AM   #5
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bathroom exhaust venting


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Originally Posted by Ron6519 View Post
The fans have a backdraft preventer. It comes with every fan. It's attached to the fan unit. You would attach the ductwork to the backdraft piece.
Ron
ok, then the only question is, is it allowed by code to attach the ducts together to exit on at the same vent cap?
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Old 10-21-2010, 10:36 AM   #6
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bathroom exhaust venting


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ok, then the only question is, is it allowed by code to attach the ducts together to exit on at the same vent cap?
sorry, I have no idea. If Gbr comes by, he'll know. You could also ask the local building dept. Codes can have a local flavor.
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Gary in WA (10-21-2010)
Old 10-21-2010, 02:28 PM   #7
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bathroom exhaust venting


Local codes......... bingo! This has been discussed before: Bath fans--how to send 2 to 1 exhaust outlet
2 bathroom exhaust fans to one outside vent pipe?
It is a local thing, really. They will have all the particulars. There are remote fan boxes with multiple inlets, factory approved. Problems arise when two different bathroom fans are on at the same time...... or when the Whole House Fan is on while a (weaker) bathroom fan is on...... etc. Ask locally.

Gary

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