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Thread: Bathroom exhaust venting: Roof or Soffit

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    DoD Army bjferri's Avatar
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    Default Bathroom exhaust venting: Roof or Soffit

    I installed my 2nd floor bathroom exhaust fan and now I have to vent it. Both the soffit and roof are easily accessible from the attic above. Which is the correct way to vent and why please.

    I prefer the soffit because fear of roof leaks.

    Thanks.

  2. #2

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    I'd wait for the pros to chime in but I'm a fan of roofing vents. Heat travels up.

    Tom

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    DoD Army bjferri's Avatar
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    Also - if it makes any difference, the soffit's are not vented so outside moisture from bathroom vent will not enter the attic.

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    DIY Senior Member construct30's Avatar
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    The code requires that regardless of how you vent the bathroom fan, it has to go to the outside. You cannot point a pipe at a soffit vent. It must have a hole cut into the soffit or roof and a proper vent cap connected to the sealed pipe. In a northern climate I like the soffit vent, but I have used both sucessfully. In old work it can be hard to get the pipe connected to a vent cap in the soffit. Also take into account how far you can run. The fan will have a chart with how much straight pipe and how many elbows you can use. If you run too far then you have to put in an in-line booster fan, in that case I head up and out the roof. Buy one of the roof vents especially for the bath fan, not just any old roof vent.

    mark

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    DoD Army bjferri's Avatar
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    If I use the soffit I do plan on cutting a proper hole to exhaust. My question is, living in NJ, is it best to vent through soffit or roof? I want to do it correct but don't want to create future problems.

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    DIY Senior Member construct30's Avatar
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    If possible and close enough, I would go with the soffit. I worry about snow and ice around the roof vents in the winter. The code says a vent from the drain has to be above the snow line for your area, and they have heat coming out of them, and yet the vents for the bathroom fans are only 5" tall and vent out the bottom. I have used the roof vents without trouble, but I don't like to. Like you mentioned, you have to install the roof vent properly or it will leak. I live in pennsylvania and I worry about the snow. Inspectors around here allow for either, but they watch the length of pipe and they make sure the pipe is sealed all the way to the outside. You should check with your local building inspector, in a lot of areas, you have to get new electrical devices and wiring inspected. Ask him what he likes to see, but I would use the soffit vent if it were my house, if possible. Is the distance to the soffit short enough for your fan and do you have the distance between the top plate and roof to get your pipe in?

    mark

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    DoD Army bjferri's Avatar
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    There's a 4' run to the soffit area, an elbow, then about a 1' run down through the soffit.

    This is how I'd like to do it.

    Other questions:

    Should I use rigid or flex? PVC or alluminum?

    Also, how and where can I put an additional damper in this run? I know my Panasonic fan unit has a built in damper, but I still fear a backdraft of cool air in the winter.

    Thanks...

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    DIY Senior Member construct30's Avatar
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    A smooth ridgid is best if possible, less restriction to flow. The charts count the flex duct as longer per foot. It also stays cleaner in my opinion. See if you can find a vent cap for a soffit for the extra damper. They have one built into the roof vent kind, but I have never been able to find one to go through the soffit with an auto open damper. Most people don't worry about it. Ask at the supply houses and home centers in your area. Also be sure to check the built in damper after you install the fan case and vent, before you put in the fan motor and light, to be sure it opens and closes freely. I've seen people drive duct screws through it when they put the vent on. I don't use duct screws, but a good aluminum tape to the fan and if I use plastic I glue the joints or use the aluminum tape on aluminum joints, not just cheap duct tape.

    I like plastic pipe over aluminum, but we have one inspector that insists on aluminum. I have never read it in a code book, but we do it to keep him happy.

    mark
    Last edited by construct30; 08-14-2007 at 10:37 AM.

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    DoD Army bjferri's Avatar
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    Thank you. I prefer pvc also. I may be able to find a damper to insert between the 4' run...

    Thanks for the tip on checking the damper - I'll do this.

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    DIY Senior Member molo's Avatar
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    some of the roof vent caps have dampers, not sure about soffit. i UNDERSTAND CONSTRUCTS CONCERN ABOUT SNOW, I LIVE IN NEW YORK STATE, MY LOCAl inspector told me the roof vent was fine (for what it's worth) they put alot of warn air out, and therefore may keep the snow off. I personally like the idea of going out the roof because the hot moist air wil travel up naturally, and the soffit vent inevitable dumps hot moist air into your soffit. if you go to the roof, you are supposed to insulate the pipe to prevent condensation from dripping down into the fan unit. if you are only 4' from a soffit then maybe you are close to your roof. i recently ran a fan to the roof (a 3' run) and used the insulated flex duct that is used for forced air systems. i secured it with the large band clamps, perhaps a couple of screw under the clamp would be a good idea to prevent it from slipping down. cutting through the roof and placing the fan properly isn't that bad, just ask!
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
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    Consultant cwhyu2's Avatar
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    Roof proper flashing no problem.

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    G.C. 22+ years(in 3 states) Old Dog's Avatar
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    Default Good advice...

    Quote Originally Posted by construct30
    A smooth ridgid...

    mark
    Good advice here...We don't have to worry about cold here in Hawaii,just rodent axcess thru the duct.We have available vent covers with dampers here.I put hardware cloth right under the covers to keep the rats out.(THey don't have any problem chewing thru the plastic.)
    I prefer soffit penetrations over roof.Less "holes" thru the roof,less chances of leaks!
    Spent part of yesterday on the two houses I'm finishing up checking vent pipe penetrations.Had to redo a couple.We have hurricane Flossie bearing down on us as I write this(about 100 miles away).Lot of rain,lot of wind,not to mention a 5.4 earthquake at 7:30 last night... rough last 24 hours in paradise!

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    DoD Army bjferri's Avatar
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    Great advice here.

    Can I ask another question regarding venting through the roof...I live in NJ, what is the best roof vent for bathroom exhaust, if there is a best, is there even an option? I see at Lowes/Home Depot the small square vent boxes that sit a few inches off the roof that have a built in damper - then in my head I see snow covering the entire gadget in the winter...is there something better?

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