Bathroom vent fans and ducting

Discussion in 'Shower & bathtub Forum & Blog' started by rfsmith48, Nov 17, 2010.

  1. rfsmith48

    rfsmith48 Member

    Messages:
    46
    Location:
    Colorado
    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
  2. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    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.
    Last edited: Nov 17, 2010
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,005
    Location:
    New England
    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.
  4. rfsmith48

    rfsmith48 Member

    Messages:
    46
    Location:
    Colorado
    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
  5. rfsmith48

    rfsmith48 Member

    Messages:
    46
    Location:
    Colorado
    Folks,

    Question answered by buying a fan from Lowes......check valve is included in fan shroud/assembly...

    Rog
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