Combine two bathroom exhaust vents?

Question

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?

Vette · Answer

Yes, that is perfectly do-able. Since the fan is AFTER the wye, no airflow issues. However, you will be having open vent between the toilet and shower area. So smells from the toilet area can migrate to the shower area (especially when the fan is off).

Answered by Vette on June 19, 2021

achao · Answer

There are some companies that make zoned bath ventilation systems if you need such precise control.
One fan unit, multiple register units at each location that has a damper control at the register. Depending which zone is turned on, the corresponding damper at that register will open to allow airflow. For example, American Aldes Vent Zone

Combine two bathroom exhaust vents?

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