Results 1 to 3 of 3
  1. #1
    Join Date
    May 2009

    Default Basement Bath Exhaust Fan Routing

    I am finishing my basement and am having trouble on how to run the exhaust fan venting. My bathroom is not near any outside wall. 1 wall is next to the stairs, the other is next to the foundation (and garage), the others are next to the family room & a bedroom.

    My first thought is to run the venting inside the floor joists to the back of the house (~25 ft) and then make a 90 degree for ~4 ft and then 90 again to the outside under my deck. Without the 2 90's I would be venting out the upstairs 1 foot overhang.
    I live in Minnesota, so I do not want to sacrifice the isolation.

    If I went up to the roof I would be looking at ~20ft vertical climb.

    The bath is not a primary bath so it would not be used much, but my fear is with the first option I would get water build up inside the pipe. Would this be OK, since it should evaporate?

    With the second option I would think that the water would just come back down.

    Thanks in advanced.

  2. #2
    Join Date
    Aug 2007
    The Great White North

    Default Re: Basement Bath Exhaust Fan Routing

    Based on where you live ... I personally would go with the horizontal run.

    Winter climates such as what you experience in Minnesota really can be problematic exhausing the bath vent through the roof. As you mentioned condensation issues can and will run straight down as well as snow covering the outside vent hood and freezing dampers open/closed. Having the vent hood mounted on an exterior wall won't have the snow cover issues and it would be easier to access the hood if it freezes.
    Besides ... the more penetrations in the roof ... the more chances for leaks.

    For every 90 degree elbow in the piping will add restriction equivelant to approx. 1 foot of length for every inch diameter of the pipe. So .... for a 4 inch 90 degree elbow would add about 4 feet of equivelant run of ducting ..... 5 inch would add 5 feet .... and so on.
    With your 25 foot run and 2 nintey degree elbows would equal to around 33 feet for a 4 inch duct.

    Here is an example of an inline fan that I have used and should work fine for your application ......

    This particular unit includes the grill , spring loaded draft damper sleeve and fan.

    In your case .... the draft sleeve would be attached to the grill ..... then the ducting running along the joist bay to the fan mounted horizontal about midway the length of the run .... then having a slight slope down to the exhaust vent hood on the exterior.
    Ideally using rigid ducting sealed with foil duct tape at all joints and keeping the elbows more gradual than 90 degrees would be the best.

    As with any type of exhaust fan you should leave it run for at least 15 or 20 minutes after using the bath room for something like a shower. This will help exhausting the excess moisture from the shower and will help with exhausting any moisture within the ducting.
    Installing a timer/ switch can be easily installed for the exhaust fan.

    One thing to also consider this exhaust fan is removing air from the living space. If this is located in your basement then it's likely you may have combustion equipment like a boiler or forced air furnace or gas fired water heater.
    Any exhaust fan will create a negative pressure while being used and could cause backdrafting on those appliances if they exhaust out a regular flue and relay on room makeup air.

    If your heating equipment is direct vented ( drawing combustion air directly from and exhausting outside ) and the hotwater tank is electric ...... this wouldn't be an issue.

    Hopefully this helps.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3
    Join Date
    May 2008
    Pacific Northwet

    Default Re: Basement Bath Exhaust Fan Routing

    Canuk brought up an important point about combustion appliances. You can provide combustion air for these appliances by running a 4" duct from outside to near the furnace or water heater. If you insulate and seal the room with the furnace, you shouldn't see too much energy loss; that room would effectively be "unheated" as if the appliances were in an attached garage.
    The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts