GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Two bath fans into same vent?

Kevin McGuire | Posted in General Questions on

I have a vented attic in zone 4c. Any other relevant info I may miss that’s needed let me know.

I have a single story home I’m working on, and it would be very easy to run both fans into the same 6” smooth exhaust vent pipe. The first runs straight out of the house with one swooping 45° In total in about 12’ all 6” smooth.

im wondering if I can tie in a second 6” smooth to that existing system. It would run about 20-30’ total, with maybe 4 elbows. Is this ever OK? Are there length requirements elbow limits etc when trying to split, or just never a good idea.

Both fans have 80 or 110 cfm.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Ethan Foley | | #1

    Nope, don't do it. You will backdraft smells from one bathroom into another and they will interfere with each others operation when they are both on. What you can do is use an inline fan to draw air from both bathrooms. That is, you can join your intakes into one but you can't join your exhausts.

  2. David B | | #2

    hmmm. I did something similar but my join was at the roof deck with a y connector. the inspector and I talked about it and he said it would be fine. Note that my vent where it meets the roof deck is about 4 feet above each fan. The y connector is right up to the roof deck as well.

    We tested this with one on and one off and both on. No impact at all. Both fans are 80 cfm running into a 4" insulated flex up to a 4" exit vent. both vents held a napkin with one or both on.

    That said, our risk is low as on vent if for in inboard 1/2 bath. So, virtually no use.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |