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#210870 - 08/13/13 09:01 PM "Y" fittings for exhaust fans
sparkync Offline

Registered: 10/17/02
Posts: 811
Loc: NC
I know this is not in the electrical code, but is there anything in the building code, mechanical code,etc.. that prohibits putting a "y" in an exhaust fan hose and running two fans to one outside vent? I know it's probably not the best, but I have a 2 story house that there is one fan vented with 6" vent and it has another fan in the same bathroom that has a 3" vent. It's a pretty long way up on an extension ladder to make another hole if it's not necessary. The fan with the 6" vent says it could have used a 4" vent, but we decided to go with the 6" for better exhaust..It is the one that has been vented to the outside eave. Thanks for the input again..

Edited by sparkync (08/13/13 09:01 PM)

2014 / 2011 NEC & Related Books and Study Guides
#210871 - 08/13/13 09:48 PM Re: "Y" fittings for exhaust fans [Re: sparkync]
wa2ise Offline

Registered: 11/29/02
Posts: 769
Loc: Oradell NJ USA
Don't know about code, but one fan's exhaust may end up backfeeding the other if both are not powered at the same time.

#210872 - 08/14/13 12:14 AM Re: "Y" fittings for exhaust fans [Re: wa2ise]
sparkyinak Offline

Registered: 07/08/07
Posts: 1288
Loc: Alaska
If you put one fan ahead of the Y should pass muster. It would draw on both of them without back feeding. Can't recite code but HRV and larger commercial systems operate that way
"Live Awesome!" - Kevin Carosa

#210873 - 08/14/13 06:14 PM Re: "Y" fittings for exhaust fans [Re: sparkync]
renosteinke Offline
Cat Servant

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Here's an idea: Let's all go to the HVAC forum for our electrical advice!

I think the appropriate answer sometimes is "I don't know, and this is the wrong place to ask."

"Fart fans" do have code requirements and proper installation rules - details that are often ignored in practice. In remodeling my house, it's amazing the number of folks who have eagerly shared their clever tricks - without realizing that their practices are against the mechanical or plumbing codes.

In practical terms, the simple truth is that unless your fan cost at least $70, and has a rigid metal duct going straight up through the roof, you're probably breaking the rules somewhere.

EVERYONE at this forum should own at least one copy - even an old one- of "Code Check Complete,' from the Tauton Press. Period.

BTW, chances are you're required to use a delay-off switch and tie it to your lighting controls.

My personal point: Don't forget make-up air.

#210874 - 08/14/13 08:56 PM Re: "Y" fittings for exhaust fans [Re: sparkync]
BigB Offline

Registered: 03/31/04
Posts: 725
Loc: Tucson, AZ USA
I can tell you that we wanted to do this exact thing on a remodel job so we asked the inspector. Turns out you ARE allowed to do it but there is a formula you use to determine the size needed for the final duct, and it IS bigger than the two from the fans. The dampers should prevent any noticeable backdraft into the other fan.

Anyway since we are not HVAC technicians we ran separate ducts out the roof.

Which brings up a question, how many of you will provide the exhaust for the fan when there is no HVAC on the job?
Or do you call in an HVAC tech and a roofer for a fart fan?

Edited by BigB (08/14/13 08:57 PM)

#210875 - 08/14/13 09:04 PM Re: "Y" fittings for exhaust fans [Re: sparkync]
HotLine1 Offline


Registered: 04/03/02
Posts: 6792
Loc: Brick, NJ USA
Did a couple over the years, both resi with no other trades on job.

Business base was 99% comm, so there were HVAC guys at the sites

#210876 - 08/15/13 02:39 AM Re: "Y" fittings for exhaust fans [Re: sparkync]
gfretwell Offline


Registered: 07/20/04
Posts: 9025
Loc: Estero,Fl,usa
I poked around in the IBC residential code mechanicals and I did not see this specifically addressed

I could be missing something. Like Reno says, this is not my field.


M1507.1 General.
Where toilet rooms and bathrooms are mechanically ventilated, the ventilation equipment shall be installed in accordance with this section.

M1507.2 Recirculation of air.
Exhaust air from bathrooms and toilet rooms shall not be recirculated within a residence or to another dwelling unit and shall be exhausted directly to the outdoors. Exhaust air from bathrooms and toilet rooms shall not discharge into an attic, crawl space or other areas inside the building.
M1507.3 Ventilation rate.
Ventilation systems shall be designed to have the capacity to exhaust the minimum air flow rate determined in accordance with Table M1507.3.
Greg Fretwell

#210880 - 08/15/13 11:07 AM Re: "Y" fittings for exhaust fans [Re: sparkync]
sparkync Offline

Registered: 10/17/02
Posts: 811
Loc: NC
Fortunately, on this particular job, the HVAC man said he would vent it:) This is the only job in a long....... time I have had a HVAC man to vent the fans. I still made need the info on other jobs though. In ordinary situations, I always vent separately, but this one was questionable... Thanks again


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