The microwave grease filter will be right at the inlet, on the bottom of the microwave. I don't see why you can't vent out the top of your cabinet if your microwave has a vent on top. You might want to put a screen of some kind on it so that something can't fall into the duct though.

How about a "real" recirculating hood such as Broan or VaH make that contains reportedly adequate filters and enough air flow rate to actually capture and contain the rising cooking plume effluent. Then put the microwave oven on a counter or use an over-the-counter model (Sharp).

That's not a good idea. The microwave has a cooling fan for the magnetron tube and uses that vent Not the exhaust vent. Hence possible damage to the microwave.

There will be grease filters on the inlet on every OTR, but recirculating modes are designed to blow the air through a second, final filter at the outlet (often with activated charcoal in it). The hope is for trapping additional grease as well as some smoke and odors.

Not sure I understood Jill's problem with having an OTR mounted flush with cabinets, but I'm wondering if the problem is that some (maybe many) OTRs need clear vertical space at the very front in order to slide up the access cover to get at the filter? If so, that would preclude a flush mount. (Unless one were set-up to lower the OTR whenever the charcoal filter needs replacing.)

So, Jill, are you looking for OTRs with a front filter cover that comes off horizontally rather than vertically?

As for adapting a recirculating system to blow out through the vertical vent stack, you can do it, but only if you are willing to be diligent about frequently cleaning the tops of your cabinets.

I recently saw such a rig when helping a friend with a remodeling project. Phenomenal grease accumulation up there. Not only in the vertical venting, but all over the top of the cabinet run and the wall immediately behind it. Mostly hidden by the raised fascia of the cabinets. Out of sight, out of mind, eh?

@tjmwine

That's not a good idea. The microwave has a cooling fan for the magnetron tube and uses that vent Not the exhaust vent. Hence possible damage to the microwave.

Can you provide more information? The magentron tube uses which vent?

Like B

jwvideo

Not sure I understood Jill's problem with having an OTR mounted flush with cabinets, but I'm wondering if the problem is that some (maybe many) OTRs need clear vertical space at the very front in order to slide up the access cover to get at the filter? If so, that would preclude a flush mount. (Unless one were set-up to lower the OTR whenever the charcoal filter needs replacing.)

So, Jill, are you looking for OTRs with a front filter cover that comes off horizontally rather than vertically?

Let me try to explain better. Right now, in order to flush mount the microwave to the 15"deep upper cabinet, I have to get a microwave where the recirculation vent blows out the front - the vent louvers are visible when you face the MW (parallel to the wall). Its pretty ugly, and the only MWs that even have that are out of date with less-than-desirable specs. I found one which will do for now - it is pictured in my OP.

All new OTR MWs now flip that recirculation blower vent upward 90degrees so that the louvers face the ceiling. This requires that the MW protrude out 2 inches past the front of the upper cabinet it is mounted to (unless you can vent to the outside, which I cannot).

If I vent using ducts meant for outside venting, then I can essentially "turn off" the recirculation mode, and cover the louvers with the upper cabinet. This will allow me to choose any MW model I want.

Hope that helps! :)

if you are using the microwave that you pictured the grill in the front is were the fan for the magnetron will blow out ( it will also be used if your turn the blower to recirculate). Most microwaves have 'hidden vents" that are on top, cleaner look, but micro would need to stick out so when the fan cools the magnetron the air will come out of those vents.

Here are some examples of the look I want to achieve. These appear to be flush-mounted to the upper cabinet. How are their magnetrons cooled?

Laurel Grove Auburn Alabama · More Info

Nashotah Transitional Kitchen · More Info

I think the key word above is "appear" because to me these OTR microwave ovens look like they are not flush by two or three inches.

From an earlier post: "If I can use the top vent [to] go up through the cabinet and resolve the
ductwork above that cabinet, that vent will care for the stove venting
and the magnatron venting, and I would not need a MW with a front-facing
louver." In my view, neither this nor any other microwave oven venting scheme I'm even vaguely aware of will "care for the stove venting" because they move far too little air per unit time and the units do not overhang the burners sufficiently. Perhaps if a supplementary blower designed for higher pressure loss is used in the path taken by the this so-called ventilation to augment the flow rate, barely adequate air flow will be possible. But even then, capture area will be too small to have much effect on front burner plume capture.

You can design for style and give up on having adequate ventilation, or design for adequate ventilation and give up on OTR microwave ovens. Your statement "For what it's worth, most of the cooking on our stove is boiling water
or soup, scrambling eggs, or simmering an occasional kettle of sauce." suggests that you can get away with doing the former. In that case, provide manufacturer specified cooling paths for the magnetron, and ignore limitations of the mediocre or worse ventilation. And don't sear steaks on the cooktop before baking them in the oven.

Hi Jill, I'm in the same boat. What is the make/model of your MW?