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I am in the process of installing an over-the-stove combination microwave/exhaust vent. I am venting it outside through the roof. I had to move the stove about 1.5 feet to the right, so now the vent pipe has a couple of turns (elbows) instead of venting straight up to the roof. On the roof there is a simple mushroom cap over the pipe to prevent water from entering.

On the top of the microwave there is a metal damper flap that opens when the exhaust is turned on. The instructions say that I have to cut the corners of the flap because I am using a Rectangular-to-Round transition adapter. Otherwise the flap may not open all the way. But I was wondering if I need the damper flap at all.

I realize that the flap is there for a purpose - basically to stop outside air from entering. However, since there are now two 90 degree bends in the pipe, and because there is a mushroom cap on top, I was wondering if the air entering from outside would be minimal.

Outside air would basically have to go up under the mushroom cap, down the pipe, take two 90 degree turns, go down through the top of the microwave, probably bend one more time inside the microwave, and finally come out at the bottom of the microwave.

Does anyone think that in that type of situation the flap is worth it? I don't think it would stop bugs from getting in, since it is partially open anyway. It's only a very thin metal flap, and it does not close all the way, except possibly in very windy conditions.

So does anyone think I should just permanently remove the damper flap on top of the microwave? It looks like it would be pretty easy to just rip it right out. Then there will be no problems with it getting stuck or not operating properly.

Any advice would be greatly appreciated.

Thanks - Joe
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