OverMicrowave venting

[Rich P]

Somehow I volunteered to help my SIL out and switch his over-the-range microwave with hood exhaust to vent the air to the outside rather than back into the kitchen over a charcoal filter.

We found a parts diagram on line (it's a GE) and there is a 3-1/2 x 10 adapter that attaches to the microwave to feed into 3-1/2 x 10 rectangular ducting. This adapter has a damper which I don't think is spring loaded.

The microwave is mounted on an exterior wall and I have found a 3-1/2 x 10 wall cap (made by Broan) that will work just fine (I think). This wall cap also has a damper which is closed by a very weak spring.

I suppose if the blowers in the microwave have enough force, having two dampers would not hurt, but then what do I know.

My question is:

Should I remove one of the dampers and if so which one?

[cabinetman]

Of the ones I've installed, there were two methods. For a non-vented, the output is fixed in the closed position. For ducted, make sure the damper is free. It connects to a corresponding shroud to the duct, which has no dampers.

Check with the instructions that came with the appliance. I've found differences in what's available online and what comes with the appliance. If you run across that, I would trust the instructions that came with the appliance.
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[newbie2wood]

It should be fine. Two dampers are common. One is activated (spring loaded) when the microwave is turned on, and one (exteranl damper) is to protect things (wasp, birds, wind) from entering your vent from the outside.
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[toolguy1000]

i have a similar GE that vents outside through the back of the microwave. i left both the GE supplied damper and a damper equipped wall cap inline and there are no problems with the unit's operation. just remember that the duct that takes odors out also lets cold air in during the winter.