Replies

1. 
   jhausch | Oct 31, 2002 02:50am | #1

   If you do, I'd recommend installing a new inline fan downstream from where the two ducts intersect into one.  That would prevent one fan from stuffing the moist air back into the other bath. 

   Then I guess you could wire it up with 3-way switches in each bath to turn it on.  But  the problem with that is if the fan is quiet enough it may not be obvious if the fan is on just by looking at switch position. 

   I don't know if this is kosher for code, but your could use regular single pole swithes if they both switched the same hot to the fan (in parallel). 

   That would mean: 

   both on(up)=fan on,

   either one on(up)=fan on,

   both off(down)=fan off

   The other option if you can't do the in-line would be some sort of flapper valve or damper on the two legs before the intersection. . . .

   Steelkilt Lives!
1. 
   BillHartmann | Oct 31, 2002 03:26am | #2

   One way to control the single fan is a double pole switch. Use the same switch to controll the lights. One pole is used for the lights in that bath. The other pole is paralled with the 2nd pole from the other switch.

   If you want the fan controlled separately then use a switch with an indicator light so that you know when it is on.

   Or use humistats in each bathroom wired in parallel so that the fans are automatic.

2. 
   BossHog | Oct 31, 2002 03:41pm | #4

   "That would prevent one fan from stuffing the moist air back into the other bath."

   Every bath fan I've seen has a flap to prevent the backflow of air from the exhaust side. Wouldn't that be enough?Progress is made by lazy men looking for easier ways to do things.

1. 
   jhausch | Oct 31, 2002 04:43pm | #5

   now that you mention it . . .you are right.  Steelkilt Lives!

1. 
   brownbagg | Oct 31, 2002 11:05pm | #6

   i did mined that way and it pass code, if fact the inspector told me to do it that way.

2. 
   Mongo | Nov 01, 2002 09:52pm | #8

   Boss got it.

   If your old fan doesn't have a backflow damper, install one in the existing line just upstream of where you cut the new vent line into the existing line.

2. 
   gordsco | Oct 31, 2002 01:00pm | #3

   If your connection is as close as possible to the roof vent, you should be okay.

   Although, if one of the bath fans is used rarely, I could see some condensate forming in the lesser used run.

   sometimes board sometimes knot

3. 
   TLRice | Nov 01, 2002 02:34pm | #7

   This is a common and acceptable practice. If you have access to the existing fan, diconnect the duct from it and make sure that it has a backdraft damper (the flap at the outlet). If there is no damper at the fan, you could backfeed exaust into that bath, though almost all bath exhaust fan come standard with a damper. If the run is long, say over 15 feet, you may want to upsize the existing duct from the junction to the roof jack. This depends on information not provided, fan capacity, existing duct size, length and configuration of the duct and the size of the roof jack. (2) 3" or (2) 4" could be handled by a single 6", for instance.