I have a tiny bathroom for the toilet, perhaps 83 cu ft adjacent to the master bathroom for the shower and tub, perhaps 1266 cu ft. Currently only the toilet has a vent with a fan. It’s being removed in the remodel. I’m adding an exhaust register to the main bathroom and I’d like to vent both rooms with a single 8” 210CFM in-line duct fan.

Since the toilet is so much smaller, should I restrict its airflow with a smaller pipe ex 3” vs the main bathroom 6”? Then have them meet at a wye before the in-line fan which would exhaust out via a 6” pipe?

Obviously I want more air to be pulled from the larger space but want to do that while maximizing the in-line fans capabilities.

Lastly, would the damper, to restrict backdraft, go after the fan or before?

  • If I understand, you want to run the toilet vent fan through the shower vent blower motor? Don't do that, have them meet in a "Y" after both blowers. – FreeMan Jun 2 at 18:39
  • Only one in-line fan for both rooms and removing the existing toilet fan. So the in-line would pull air from both rooms. – DIY Tom Jun 2 at 18:56
  • ah, gotcha! You may want to edit your question to help make that more clear. Some formatting and line breaks will help with that, too. – FreeMan Jun 2 at 19:01
  • 1
    Thanks! Gave it a touch up! :) – DIY Tom Jun 2 at 19:13

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