Bathroom vent fans and ducting

**rfsmith48** · 11-17-2010, 11:37 AM

Folks,

I am adding vent fans to 2 adjacent bathrooms. Fans will dump into 1 four inch vent pipe.

Questions: does anyone make check valves for this type of tubing? (Don't want one running fan to dump into other bathroom) Local hardware store recommended a y-pipe to minimize problem, don't know if that works well or not?

Thanks in advance.

Rog
303 494 0140

**Thatguy** · 11-17-2010, 04:53 PM

Originally Posted by rfsmith48

Fans will dump into 1 four inch vent pipe.

Questions: does anyone make check valves for this type of tubing?

So each fan will see the equivalent cross section of a 2.8" dia. pipe if they both run at the same time. The backpressure seen depends on the relative length of each leg of the Y. Exterior louvered wall vents act like leaky one way valves but you'd have to modify them for inline use.

It might work because bathroom fans seem to be oversized; you only need 8 air changes per hour so a 5' W x 7' D x 8' H room only needs 37 CFM.

If you can pry the "fan curves" from the fan manufacturers this duct network can be analyzed and so your fan performance can be predicted ahead of time.
Don't forget to undercut the bathroom doors to admit new air.

**jadnashua** · 11-17-2010, 06:06 PM

I'd consider a remote fan designed to handle multiple rooms. Fantech, among others, make some designed for this sort of application. Dampers often leak...you might end up dumping the output from one bath into the other rather than outside and sharing the moisture and smells.

**rfsmith48** · 11-17-2010, 06:26 PM

Guys,

Thanks for the responses. To clarify:

1. Primary concern is: One fan running and blowing its output into the other bathroom.
2. Secondary concern: Both fans running and pushing air into a 4" pipe. This is a lesser problem and low probability for both showers being used simultaneously.

Still searching for check valves for 4" duct pipe....

Thanks,

Rog