Venting the microwave oven

Old 05-03-21, 06:48 PM
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Venting the microwave oven

Hello, thanks for taking the time to read my post.

This morning my wife and I had our microwave go belly up. We bought this as a replacement: Fingerprint Resistant Stainless Steel 2.1 cu. ft. Over-the-Range Microwave with Steam cooking WMH53521HZ | Whirlpool. Upon starting the installation, I discovered there was no proper venting for the microwave, instead the ventilation was basically blowing upwards into the kitchen (which, I'm assuming, is more common than I assumed). I'm no expert in this matter, but it seems like such a thing would be better to vent outdoors instead of upwards and into the kitchen itself. Maybe that's common?

I took a video here:

My question is this: given the layout of the kitchen and dining room, does it make sense to worry about installing or fixing the ventilation? More specifically: is being able to vent the airflow from the microwave outdoors even possible? Are we talking about a huge project?

I'm sorry if my questions are rather vague, but I've never really studied proper ventilation of these things before. Thanks.

Old 05-03-21, 07:10 PM
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Venting back into the room is fairly common since venting outside can be difficult.
It is definitely recommended to vent outside especially if you have a gas stove.

It's hard to tell from your video but it looks like the wall behind the microwave is not outside.
It is usually fairly easy to vent straight out of the back of the microwave to outside.
If venting straight outside is not possible then going up to the roof would be the next best choice.

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Old 05-03-21, 07:13 PM
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Your instructions give you the option to install it in recirculation mode... wall venting... or roof venting.

See the section in the installation instructions:

Rotate Blower Motor

"The microwave oven is set for recirculation installation. For wall
or roof venting, changes must be made to the venting system.
NOTE: Skip this section if you are using recirculation installation.
Keep the damper assembly in case the venting method is
changed, or the microwave oven is reinstalled in another location
where wall or roof venting may be used."

-end quote-

So in short, it is up to you.

As for whether or not its a huge project, it depends on your skill level. It will involve drywall work, painting, duct work, some framing alterations, some HVAC ductwork, access to the attic, some insulating, firestopping, and roofing.

(You will likely need to go up through the roof, not out through the side wall)

Personally, since you have no existing ductwork for it, I would keep it on recirculate.

And that duct hood on your exterior wall is likely a code violation as its within 3 feet of an operable/nonoperable window. (M1506.3)
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Old 05-03-21, 07:21 PM
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Man, both of you are absolutely brilliant. Thanks for the input.
Old 05-04-21, 04:49 AM
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FWIW...All range hoods should be outside vented. And I think that is the trend in todays house building. But for those of use stuck with recirculation, not much we can do. Because of that we hardly ever use the vent fan. And those charcoal filters are about as useless as can be.
Old 05-04-21, 04:49 AM
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My wife is an amateur chef so a proper, vent to the outside hood is a necessity. Unfortunately most over the range microwaves are pitiful vent hoods. If you vent outside it is important to keep the duct run as short and as straight as possible to minimize flow resistance.

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