2 Bathrooms, 2 Vent Fans, 1 Duct?

I'm converting a single bathroom into two (both on 2nd floor), and I've currently got only one bathroom fan vent that penetrates the roof. Since the new bathroom ventilation fans I purchased each has a backdraft damper, can these fans be tied into a common vent line, or does each fan need an independent exhaust point to the roof? I doubt both fans will be running simultaneously, but it could happen. (I didn't want to go with the multiple point, single in-line fan route.) Working with 4" ducts.

Thanks,
dgillespie

 

I actually have the exact same question and have been pouring over the IRC codes to find an answer. I can't find any specific on bathroom vent specs in the IRC.

I don't think the concern would be when both fans are running since the past of least resistance for both fans would be to the exit, not into one fan from another. The worst that could occur in that situation would be the rated CFM of the fans would be reduced unless the vent pipe was increased in size.

I'm more concerned with the effectiveness of the damper at preventing backdraft from one bathroom to the other.

Of course all of this discussion is moot since we really need to know what the code allows.

Mark

 

dgillespie,

Here's one option,

http://www.fantech.net/bathroom.htm

Hope this helps!

 

Hey Doug, thought I'd chime in on this one since I happened to do this once.

I tied two vent fans together in the rafters with a wye connector since the homeowner refused to go through the roof twice.

The result? If both bathrooms were in use, no matter what the use, the other one could always smell what the other was doing, whether using the toilet or taking a shower. The link provided above resolves that issue instantly with no ability to send the foul air back to the vent fan not in use.

 

Thanks for the feedback. Since I've already bought the fans, I'm probably not going to switch to an in-line. Plus, the in-line pulls air out of rooms that I'm not using, so it may not be the best energy-efficient solution. I plan on connecting the two fans as close to the exhaust vent as possible, and then I'll put another penetration in the roof once the snow melts if I run into problems.

 

I spoke with my local building inspector and he is okay with allowing me to connect to exhaust fans to one 4" duct as long as they have flapper valves, which almost all of them do.

Mark

 

The upstairs bath in my house has a 5*5 toilet/sink room and a 5*5 shower room. The original fan was in the toilet room and there's no window in the shower room. I definitely put in another fan in the shower room as soon as I could. I found a 'Y' (2 3" in holes and 1 6" hole) at a habitat reuse center, attached that to the 6" vent that was already penetrating my roof, and then put the two vans on the same circuit and added a three way switch (thus the fans are operable from toilet room or shower room). I'm sure it pulls more air than it should but there's no worry of backdraft etc.