Sealing microwave exhaust duct


I am nearing completion of a kitchen remodel. I am wondering how you have dealt with sealing the exhaust fan port to the ducting going to the attic.
I was able to thoroughly seal the exhaust port to the top of the oven with foil tape prior to mounting the microwave. The microwave has to be mounted before the duct can be attached to the exhaust port. Unfortunately, because of the limited space around the cutout in the cabinet, I can't seal the joint between duct and exhaust port with the same foil tape.
Any ideas?
Gordon Shumway
Our Constitution needs to be used less as a shield for the guilty and more as a sword for the victim.
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Usually the microwave comes with a flange with the damper attached and that goes into the ductwork. I don't think you need to seal where the microwave meets the ductwork. I don't think its possible anyway since there is no room to seal it once the microwave is installed. From memory, I don't think my installation manual metions it.
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Never heard of directly connecting a uwave to an exhaust. My experience is that the exhaust fan in a uwave isn't nearly strong enough to exhaust thru any reasonable duct length.
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hr(bob) snipped-for-privacy@att.net wrote:

If it doesn't have an exhaust connected, where is the exhaust going to go? Back into the kitchen? That would be idiotic.
Mine exhausts fine.
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All the countertop uwaves I have ever owned or seen do exhaust back into the room in which they are located.
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wrote:

Not a countertop, an over the stove. And if you look at the way the exhaust fan is setup on most of them you will see that it can be removed and reinserted such that it now exhausts straight up. If you have duct work installed above it you can vent it outside instead of just recirculating the air
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hr(bob) snipped-for-privacy@att.net wrote:

This is obviously not a countertop uwave. The exhaust fan is for the stove under it.
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On Sun, 16 May 2010 17:50:54 -0700 (PDT), Mikepier

Yes, mine had the flange with the damper. That's what I was calling the "exhaust port." I was able to seal the exhaust port to the exterior sheet metal of the oven with no problem. When I put the 3-1/4x10 duct over the exhaust port (flange) it just fits over the exhaust port somewhat loosely. It fits as snugly as can be expected with no other components. There is a noticeable rush of air inside the cabinet coming from that joint. I never noticed that type of air leak with the old unit. However, the fan on this one seems to much more powerful than the old one.
Gordon Shumway
Our Constitution needs to be used less as a shield for the guilty and more as a sword for the victim.
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All the microwave/fans I've seen has the flange attached to the unit with the fastening tabs. I don't recall any in which you seal the flange to the unit. Read the instructions that came with your unit and see what it says, but I'm pretty sure the flange stays on the unit with no sealing. Make sure your unit is configured to blow air out the top. Some units you have to re-orient the fan inside depending on whether you want to blow air out the top or side
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*One microwave that I removed a year or so ago had weatherstripping around the duct edges on both the wall and microwave oven. First time that I saw that.
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That's how I do it. You can get that 1/2" by 1/2" foam that is sticky on one side.
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