Dryer vent pipe does not go all the way to the roof in attic

Discussion in 'Remodel Forum & Blog' started by Reniassance man, Jul 13, 2005.

  1. Reniassance man

    Reniassance man New Member

    Messages:
    3
    Location:
    British Columbia
    The vent in the roof has a screen in it.The pipe is four inches away from the vent in the attic. Do I need to replace the vent with one with a flap or can I just get a flange and connect to the existing vent with the screen? is the screen going to collect too much lint? Can some one help? Thanks. Reniassance man
  2. captwally

    captwally New Member

    Messages:
    102
    Location:
    Florida
    I guess I'm not quite sure what your question is. If the vent from your dryer to the roof has a 4 inch gap, you need to close that gap. I had a similar experience back in 95 after my house was built. The vent tube was not well attached to the vent on the roof, which had a flap and a screen. But one day I went into the attic and found lint all over the place! The tube had fallen off the roof fixture and the dryer was venting into the attic. I secured it back on with A/C foil tape and then fastened it to the nearby rafter with some wire and duct tape. Worked like a charm.
  3. Reniassance man

    Reniassance man New Member

    Messages:
    3
    Location:
    British Columbia
    Is it just that simple?

    Thanks Wally,
    The vent that is on the roof now has no way to connect the vent pipe. The pipe is just pointing at the vent with a four inch gap.The question is If I put a flange to connect the pipe is the present screen going to collect lint? is this going to be a problem? Do I need to seal the flange that connects the round pipe to the square vent- the vent is on the outside the flange/adapter would be on the attic side. Should I cut the screen so that no lint will catch on the screen? Any input would be good.I still am a little confused.
    Thanks
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,485
    Location:
    Cave Creek, Arizona
    vent

    The screen will definitely collect lint. Usually we install a "T" top vent and fasten the dryer vent into it, but if you use that one, then cut the screen away and then secure the pipe so it cannot fall down.
  5. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Venting a dryer vertically thru the roof, although it is done. probably voids the warranty on the dryer; and it will definitely affect you energy usage: it will take much longer to dry a load.

    Check with your manufacturere to see what the maximum vertical run of pipe allowed is.
  6. captwally

    captwally New Member

    Messages:
    102
    Location:
    Florida
    Now why is that, Jimbo? I've never heard that, and though I'm not disagreeing with you, I'm just curious. Surely there's a logical reason. I would think it would be more efficient, as hot air rises. True or a moot point? Thanks
  7. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    I'm with Captwally all the way here. There are literally thousands of homes with a dryer's vent pipe thru the roof. And no problems.
    There are roof flashings with termination point flappers that will prevent any "backdrafting" or weather to come in.
    Imo, running the vent out the side wall or soffit is the best, but going vertically up and thru the roof is still an ok installation.

    IT WILL NOT VOID the dryer warranty,as long as the total running distance (equivalant length) is within the dryer's specs.

    DO NOT install any lint screen at the termination point. The lint filter that is at the dryer should be cleaned periodically. Use the smooth plain metal pipe (not the corrugated stuff)
    Last edited: Jul 15, 2005
  8. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I agree that there are thousands ( maybe millions of dryers ) installed this way. I don't agree that they work well. I cannot now put my hands on a manufacturers spec. The closest I can find is from Maytag: they specify that the static pressure at the dryer outlet must not exceed 0.92" WC. I do not know what this would translate to in terms of height. But it is clear that the length of exhause duct and the height of the termination both affect air flow thru the dryer and thus the efficiency.

    Generally, people are stuck with the installation which their builder provided, so that is a fact of life. And for the homeowner who asked the original question, I am sorry we drifted off track for you. The important answer to your question is that the moisture and lint filled air from your dryer must get outside. To allow any of it to settle in the attic is a big problem. The moisture is an obvious mold issue, and the lint is a fire hazard. Be careful about a screen at the termination, because sooner or later it will be a problem. A cover called a "wagon cap" is probably the preferred item for you.
  9. captwally

    captwally New Member

    Messages:
    102
    Location:
    Florida
    Actually, Jimbo, I think getting slightly off the track is one of the primary benefits of a forum such as this, which is why they call it a "thread." It tends to weave around a bit and generates productive conversation in relation to the solution to a topic. After contemplating and reading the conversation, I think I see the point, though as we know, most likely, millions of homes have the dryers vented in this manner. Hot air does rise, but all air, hot or cold, has friction, whether forced or just lightly pushed as the case is in a dryer. I wonder out loud, if a larger diameter pipe could be used in the vertical exhaust? Many homes are designed so that the length would be the same to reach the outside, whether it is vertical or horizontal...? Any thoughts?
  10. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I agree. Air is a fluid, just like water, and the rules of physics apply. So, I agree with the suggestion to use a larger size to reduce friction. The install charts from all the manufacturers give maximum lengths; in all cases the max. allowed is reduced as the number of elbows increases, and the max. is also less for flex pipe than for smooth wall rigid. SO I think we are all in agreement on the types of things that affect performance and the things that can be done to minimize friction and back pressure.
  11. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,328
    Location:
    Yakima WA
    Does the vent have any kind of a pipe connected to it or is there a way a short pipe can be attached to the vent? What I'm think is to use a short length of flex pipe to make the transition from the vent to the pipe. This would be easy to do if there is a stub of pipe on the vent. You'd only need a inch or so. The vent has to go outside not matter how you do it. I don't like a screen in the vent itself, it never gets cleaned.
  12. Reniassance man

    Reniassance man New Member

    Messages:
    3
    Location:
    British Columbia
    :) Thanks for all your feed back. The plastic flange to connect the pipe to the vent is the final answer with the screen removed from the vent already on the roof. The flange I found however can only be purchased with the vent. The vent should not be used for the dryer but the flange can be removed easy and placed in the attic at a price of ten dollars canadian and trow away the vent.
  13. toolaholic

    toolaholic General Contractor Carpenter

    Messages:
    874
    Location:
    Marin Co. Ca.
    what is scary

    is the chance you are dumping moisture in the attic

    CAN YOU SAY MOLD ? give attic a good look
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