We have a dryer vent in our apartment that has a couple of twists and turns (due to the design of the floor plan) on its way out to the roof to vent. The twists have been done by elbow joints covered by aluminum tape.

Unfortunately, due to the cold temperatures outside, the hot, moist air in the vent leaks out through the elbow joints and creates condensation drips (which pool and leak over a period of time when the dryer is in operation).

(Re-routing the vents to keep them straight is not an option because of the design of the house)

What are some options to completely seal the vent, and specifically the elbow joints?

  1. Is there any sealant that can be applied on the outside for waterproofing to prevent the condensation leak?
  2. Is there "better tape" (other than typical aluminum tape) that can do the sealing?
  3. If the elbow joint needs to be replaced, is there any product that can create a good seal?

Thanks in advance for your help!

  • 3
    Good enough to make them water tight from the moisture that's condensing inside before it leaves the flue? No. IDK how to solve that problem (it sticks too far out of the roof? usually dryer vents are out a wall). There's no obstructions? - They usually clog themselves with fuzz with at least a half decent tape job. Your problem is it's dripping water that shouldn't be there.
    – Mazura
    Commented Jan 8 at 16:07
  • 5
    I agree with Mazura that you can't expect to turn your duct into plumbing. Maybe insulate it to reduce condensation inside the structure?
    – isherwood
    Commented Jan 8 at 16:11
  • The "typical aluminum tape" is typical because that's the proper tool for sealing duct work. There are mastic sealants, as well, but aluminum tape is quick and easy.
    – FreeMan
    Commented Jan 8 at 16:11
  • 1
    Also make sure the exit point has a flapper to keep cold outside air from coming back down the vent when you're not actively using your dryer. It's possible there's fuzz caught in the flapper that's keeping it from sealing well, which will cause excess cold air from coming back into the vent, causing condensation and energy loss.
    – Milwrdfan
    Commented Jan 8 at 18:32

1 Answer 1


You need a sealant which can withstand the anticipated high temperature of your dryer for prolonged periods of time.

Not an endorsement (I've never used it):

Red Devil HVAC Caulk Extreme Temperature Silicone can withstand -60°F to 400°F

enter image description here

  • 1
    Standard silicone is rated to several hundred degrees already. Nothing is that hot in an attic and there's no need for expensive specialty products. That said, it's a fool's game to try and make an exhaust duct into plumbing.
    – isherwood
    Commented Jan 8 at 16:10
  • @isherwood Which silicone?
    – MonkeyZeus
    Commented Jan 8 at 16:13
  • Any. They're all nearly the same thing (if labeled 100%).
    – isherwood
    Commented Jan 8 at 16:15
  • @isherwood I'd hate for OP to introduce a non-compliant duct sealant into their apartment. All my efforts are returning that at minimum you'd want RTV silicone for HVAC such as the one DAP has.
    – MonkeyZeus
    Commented Jan 8 at 16:26

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