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Thread: sealing around dryer vent exit

  1. #1
    DIY Member maddfrog's Avatar
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    Default sealing around dryer vent exit

    I recently installed a new dryer in our laundry room/bathroom. The room is extremely small and the dryer needs to be pushed flush to the wall. The vent exits to the rear, straight through wall and into the garage. It then turns 90 degrees, runs about 60" along the inside of the garage wall and then turns 90 degrees more and exits through the garage wall to the outside of the house.

    I was hoping that someone could suggest a way to seal the opening around the vent pipe where it enters the garage. Because of the tight fit, I had to attach the straight piece to the dryer with a clamp and seal it with foil tape before I pushed the dryer back tight to the wall. If I need to move the dryer for any reason, that straight pipe needs to be able to slide back into the room along with the dryer (after I disconnect the elbow in the garage of course)

    The local appliance supply shop couldn't come up with anything except expanding foam, which won't work for me because it'll fix that straight piece in place. Is there some kind of gasket or trim ring that can be used on the garage side around the pipe? It's a sheetrock wall...

  2. #2
    Rancher
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    Wrap the dryer pipe in plastic, several layers, then put the foam around it, it should be able to slide in and out with an almost airtight seal.

    Rancher

  3. #3

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    I'm no expert on codes, but it seems to me that your vent has too many 90's and you will have quite a lint build-up at the last turn.

  4. #4
    Plumber jimbo's Avatar
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    Stuff as much fibreglas insulation as you can around that pipe penetration.

    I count 2 90's which is not a big problem.

    This is a firecode wall, and the dryer penetration may violate that.

  5. #5
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Here's a general reference:

    http://resourcecenter.pnl.gov/html/R...nter//132.html

    I've got 2 90s in my dryer run, which goes 8' up, then 8' horizontally (actually sloped downward, treated like a waste pipe, since water vapor will condense in the pipe). I couldn't find the specific code reference just now, but I checked it when I installed it, and it complied. Many codes just say to follow manufacturer's recommendations, which I did. Look in your dryer's installation manual.

    Update: Here's a reference to the Massachusetts 1997 code, FWIW: http://www.mass.gov/bbrs/780CMR_Ch3618.pdf

    As for the wall problem, I'd foam or better yet, caulk (with fireproof high-temperature caulk), or maybe best, mortar a piece of metal duct just a smidgeon larger than the real duct into the wall. Then the real duct could slide in and out of the larger one. You could leave enough of the outer sleeve sticking out of the wall in the garage to use to duct-tape the two together to prevent air or bug intrusion.

    If you're using 4" metal pipe for the dryer vent, get a piece of 5" duct and trim off the interlocking joint bends on each side. Wrap it around your 4" duct, with the desired slop. Tape up the joint with metal duct tape. Slide it off, install it in the wall, and viola!
    Last edited by Mikey; 10-27-2006 at 02:15 PM.

  6. #6
    DIY Member maddfrog's Avatar
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    Thanks for the ideas. I'll have to ponder them a bit.

    I do know that two 90s is acceptable, so I'm not worried about that. Unfortunately, it does slope slightly upward, but there's not much I can do about that without cutting into the sill of the garage wall and taking a bite out of the footer it sits on. I was replacing an existing installation, and I don't really have any other options for routing it.

    Even with the issues I have now, it's a huge step forward from what was there. The problems started at the dryer, where the previous owner used a flexible duct and relied on it to expand and contract when you moved the dryer; however, when you pushed the dryer to the wall, all the flexible vent did was crimp itself until it's diameter was about half the intended size. After that, the vent entered into the garage, where it mated with a rigid aluminum duct that also had a big crimp in it and was supported at the ends by the holes in the wall and in the middle by elastic bandages wrapped around it and tacked to the wall. The rigid duct re-entered the wall thorough an opening that was surrounded by duct tape. When I pulled it out, I found that the other end was no longer attached to the vent cap, so the wall was full of lint and mold - ugh. It's a wonder the house never burned down.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    Just a comment for others reading this...avoid using a flexible dryer hose. It will cost you money with increased resistance (slows the air down), and collect lint, which will create a fire hazard and further decrease the air flow. All of this costs you more, since the dryer needs to run longer and risks setting the lint on fire - use smooth walled rigid ductwork and avoid as many elbows as you can.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8
    DIY Member maddfrog's Avatar
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    That's a good point and I wholeheartedly agree. The flexible duct that I was replacing came with the house and it was mated with dented and crimped rigid aluminum ductwork. It was pretty full of lint all the way through.

    No idea how long it was there, but after replacing the entire duct, end to end, with rigid galvanized ducting, there is a noticable difference in the airflow through the vent. Clothes also dry in about 2/3 the time.

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