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Most of the duct dampers don't provide 100% seal from air flow. The below picture might be. I have collar with damper, But its just not enough to stop/bypass the air flow.

what is this called in the picture highlighted, Fiber stripping, what kind of it is ?

It seems the strip is glued to the metal. enter image description here

thanks!

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It may be a simple weatherstripping that was added.

It is rare to completely block a trunk line. In fact I have seen trunk lines split open because they were blocked off. The home owner did not understand what he was doing when trying to convert a multi level home from 60-40 to 40-60 and split a large duct in the wall.

In another case the blocked both main trunks with the fan on and it split the duct from the Y to the furnace.

The few times I have done this is for garages or basements not normally conditioned so a more positive or complete seal is made.

To do this I have used weather stripping. I have used silicone, but have found metal riveted in place with a compliant rubber stays in place and seals better.

The quality of the seal and how well it is installed can seal close to 99% and self adhesive sponge rubber seals can do as good but don’t last long and can blow out with higher duct pressures.

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  • Thanks. So what you are suggesting is use any weather stripping and the seal it with a silicone ? I'll have to make sure the stripping works in extreme weather and is also fire retardant. can please you recommend a link?
    – PowerTech
    Commented Jun 3, 2021 at 19:07
  • Will this work? it seems open cell homedepot.com/p/…
    – PowerTech
    Commented Jun 3, 2021 at 19:34
  • Vicky that foam will work it works well for a couple of years then needs to be replaced but it is inexpensive and works.
    – Ed Beal
    Commented Jun 3, 2021 at 20:03
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    I used door seal like a metal strip that has a rubber strip that is soft and round the door closes on it usually nailed in, I used a touch of silicone and pop rivets that seal is a life time verses the foam that works but breaks down.
    – Ed Beal
    Commented Jun 4, 2021 at 1:02
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    Neoprene would work but is usually fairly stiff. Putting 1/2 on one side from the pivot and 1/2 on the other side from the pivot will work as it allows the plate to move away from the seal points. Make sure to allow any sealant / glue to dry prior to trying to close the damper under pressure. Although you may only have a couple of inches water Column pressure a 8” duct has a lot of force and will move the seal (a mistake from years past), I rivet because I can’t wait 3-4 hours for the sealant to cure.
    – Ed Beal
    Commented Jun 8, 2021 at 22:37

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