bathroom exhaust vent sizing

Discussion in 'Remodel Forum & Blog' started by mchristo, Nov 23, 2009.

  1. mchristo

    mchristo New Member

    Messages:
    17
    Location:
    New Hampshire
    I'm remodeling a small bathroom for a summer cabin. the bathroom is 9 x 5 feet x 8 feet high. In summer I get humidity problems in the house and in particular in the bathroom. currently there is no vent fan. I'm planning on installing one now. I'm thinking about over sizing the cfm's on the fan and putting it on a timer to vent the house when I'm not there during the week.

    I'm thinking that in the summer that would be fine, but in winter it would push out all my warm air and draw in cold air whenever it is turned on.

    What would the standard cfm be for a 9x 5 bathroom, and how much over that would you go for my humidity problem.
  2. mchristo

    mchristo New Member

    Messages:
    17
    Location:
    New Hampshire
    Another bath fan question

    should I have a fresh air return in the bathroom, or let it draw in from various leaks in the rest of the house?
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,889
    Location:
    New England
    Panasonic has a calculator on their website to help with this.

    Keep in mind that the vent size, length, and number of elbows will reduce the rated CFM of most fans. the max turnover you probably want to accept is 10x per hour. With the size room you have 360cuft. Multiply that by 10x in a hour = 3600 cu ft/60 minutes = 60CMF.

    It somewhat depends on whether you are running the a/c or heat where you want to draw that air from. It also depends on how tight the cabin is and if you are running any combustion devices like a gas stove, dryer, or furnace. All of those need fresh air, and if the fan is running, you don't want to starve things and possibly cause a backdraft.
  4. GabeS

    GabeS Remodel Contractor

    Messages:
    294
    Location:
    Brooklyn NY
    or carbon monoxide.
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