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Old 08-13-2019, 09:02 AM
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Microwave venting - expert opinions needed, other opinions welcome


Iím currently have the kitchen in my apartment remodeled. And my contractor did something different from what I approved. And I donít think I like it but itís going to be a pain to fix. Iím trying to get opinions from someone that knows HVAC.

I have an over the range microwave. The building vent outlet is near the ceiling, on the perpendicular wall, about 6 feet away.

When we were planning, my contractor told me he was going to mount the cabinets a couple of inches below the ceiling, run the hose up through one cabinet and cross it over the top of the cabinets to the vent outlet.

I approved this. But when I got back into my apartment the cabinets were flush to the ceiling. I asked him about the venting. He said that since the microwave had a recirculating air feature he didnít need to vent.

I did NOT like this. The kitchen is small and located in the back of the apartment, far from any windows or natural ventilation. It is open to the living room - 3/4 of the space is an L shaped open living area with the kitchen comprising the short side of the L. Itís a dead end with no ventilation and I donít think the recirculating fan is going to be enough to clear cooking smells. Plus, this is going to be a rental. And Iím making the kitchen really nice ( with high end appliances ) in the hope of getting a slightly higher than median rent. My kitchen may attract someone that cooks a lot. And I donít want to deal with filters and rental tenants.

So my inclination is to make him go back in and drop the cabinets to the height I approved and add the vent hose.

But am I making a big deal over nothing? Part of me thinks do but the other part says I have a right to get what I approved and I shouldnít feel bad about making a fuss.

Opinions?
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Old 08-13-2019, 09:16 AM
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Is the MW capable of exterior venting? In that case yeah it’s a big deal. Recirc is not a good option imho. The contractor bid the job with venting, don’t let him try to charge more now that he didn’t do it as agreed.
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Old 08-13-2019, 10:07 AM
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I would prefer exterior venting over the recirculating type, so I agree that you should make the contractor fix it, particularly as that's what he agreed to.
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Old 08-13-2019, 10:40 AM
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I have installed many microwave ovens, built in or over the range, and project managed many kitchens. This was not the contractor's decision to make and is poor customer service.

Pretty much all OTR microwaves can be configured to recirculate the exhaust rather than vent it. This is not a desirable function for a range 'hood', but a make do feature for situations where proper venting is not possible. All this does is remove some of the grease and oil with the unit's grease filters but does not do anything about smoke, water vapour, or odours.

Venting an OTR microwave can be much more expensive than the microwave itself. There is not only the duct work, but milling cabinetry, insulating, possibly installing exhaust hood on roof or wall. Just the install of the unit itself with out any venting can be a couple hours labour for a carpenter and actually placing the unit should be done with two people so a helper is necessary too. On bigger projects quite often multiple trades will be involved.

I suspect contractor only estimated for install and did not put in enough money for the rest. He should have at least discussed this with you instead of installing in a configuration you did not agree to.
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Old 08-13-2019, 10:46 AM
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Also, what do you have in writing and are you prepared for pushback and going to court? Do you have a written description of what was supposed to have been done and or a blueprint?
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Old 08-13-2019, 10:52 AM
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Are the cabinets actually higher or did he simply build a bulkhead up to ceiling? Standard cabinets are typically 30" high, tall cabinets are 39" and an upgrade. Both would typically 18-20" above countertop. Fire code is minimum 18" to combustibles at the edge of the range.

Normally there is a drawing that customer would agree to.
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Old 08-13-2019, 12:08 PM
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The cabinets currently go to the ceiling, I was under the impression that they are 42”, which is what he told me was a standard size. No bulkhead, they were going to put in a strip of molding to clean everything up.

But because he put them to the ceiling, they are also 3” higher than than we had decided, there is a clearly marked pencil line on the wall behind the fridge ( we haven’t painted yet showing the height we decided on. And they are higher than that. When they are moved down they will be st the same height as the old ones.

I’ll confess, there are a lot of details I don’t have in writing. But I don’t think I’m going to have a legal problem, I believe they are in my apartment dropping these down right now. It’s a small kitchen and there only 6 cabinets and one filler piece that need to move.
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Old 08-13-2019, 04:21 PM
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It's not that hard to pull upper cabinets and reposition them. They're just screwed to the wall. A recirculating fan is useless for cooking. I'd make him do it the way he said he would.
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Old 08-14-2019, 01:21 AM
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Depending on where you are, a non-vented range hood/microwave may be a violation of local building codes. You’d need to check with your local building department for the local rules.
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Old 08-14-2019, 01:30 AM
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Sorry, I don't understand why does the microwave need to vent to the outside. I know they need to have airspace around them for cooling, but what are they venting other than normal-kitchen-composition hot air?

It may be a language issue, I'm used to thinking of "venting to the outside" to refer to dangerous gases only (in my local construction code and in domestic contexts you need low vents for butane and propane kitchens, high vents for natural gas, because that's the location which helps avoid accumulation of those specific gases; electric kitchen, no vents needed).

Last edited by Nava; 08-14-2019 at 01:32 AM.
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Old 08-14-2019, 03:54 AM
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Quote:
Originally Posted by Nava View Post
Sorry, I don't understand why does the microwave need to vent to the outside. I know they need to have airspace around them for cooling, but what are they venting other than normal-kitchen-composition hot air?

It may be a language issue, I'm used to thinking of "venting to the outside" to refer to dangerous gases only (in my local construction code and in domestic contexts you need low vents for butane and propane kitchens, high vents for natural gas, because that's the location which helps avoid accumulation of those specific gases; electric kitchen, no vents needed).
It's an Over The Range Microwave, the venting is for the range (stove) below, not for the Microwave, to expel cooking smells to the outside rather than running it through a filter and then recirculating it back into the living space.
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Old 08-14-2019, 09:40 AM
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The resolution is that they found a way to vent by going through the ceiling. This will connect to the “building ventilation system”, as it were.

The building ventilation system seems to be based on roof fans that draw air up from the empty ceiling/wall spaces between apartments. All kitchens and bathroom without windows, like mine, have a small grilled opening that connects to this space. The public hallways also have these grills. But there is no actual ducting, so as long as they can vent into the ceiling I should be fine, I don’t have to get a duct to the actual vent grill location.
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Old 08-14-2019, 09:44 AM
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Quote:
Originally Posted by FluffyBob View Post
Are the cabinets actually higher or did he simply build a bulkhead up to ceiling? Standard cabinets are typically 30" high, tall cabinets are 39" and an upgrade. Both would typically 18-20" above countertop. Fire code is minimum 18" to combustibles at the edge of the range.

Normally there is a drawing that customer would agree to.
Just a correction to my earlier post.

You are right, the cabinets are 39”. The 42” that I had in my head was the distance from ceiling to bottom of cabinet, including the 3” space between cabinet top and ceiling. That space was eliminated.

Last edited by Ann Hedonia; 08-14-2019 at 09:45 AM.
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Old 08-14-2019, 06:49 PM
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I recently had my kitchen remodeled and as part of it I had them add an external vent for the microwave hood when I discussed it with the GC. The carpenter came and said "Are you sure you want to do that? Microwave vents are pretty useless..."

I had him do it. Based on my observations, he was quite correct. A microwave simply does not draw enough air through its ventilation system to handle the smoke/steam coming off of a typical range. I am considering adding an inline fan to help draw more air out.
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Old 08-14-2019, 10:07 PM
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Quote:
Originally Posted by Nava View Post
Sorry, I don't understand why does the microwave need to vent to the outside. I know they need to have airspace around them for cooling, but what are they venting other than normal-kitchen-composition hot air?
As others have mentioned, microwaves designed to go over the range often have a
small, weak fans to approximate the ventilation hoods common in commercial kitchens.

So itís less a ďmicrowave ventĒ than a microwave with an extra fan that pulls air from above the range. I understood the OPís phrase but I can see why it could be confusing to someone who hasnít spent a ton of time in an American kitchen.

Cooking that generates more than a wisp of smoke often sets off fire alarms, which is pretty annoying and disruptive. I applaud the OP for getting the contractor to find a way to vent the fan exhaust to the outside. That fan doesnít move much air, but pulling a little smoke out is a whole lot better than the alternative. The recirculating mode is worse than useless.
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Old 08-15-2019, 04:55 AM
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I'm with Nava - I have a hard time visualizing the situation. How high is the microwave above the stove?
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Old 08-15-2019, 08:10 AM
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If it is a gas stove I would certainly want external venting since the output is poisonous. Also, aside from lingering cooking smells, steam and foggy windows would be an issue. Glad it was worked out properly.
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Old 08-15-2019, 11:29 AM
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Quote:
Originally Posted by Alessan View Post
I'm with Nava - I have a hard time visualizing the situation. How high is the microwave above the stove?

Here is a good photo that shows one. It wasnít the most attractive photo in the gallery, but I picked it because it actually shows the vent system at work.

https://www.google.com/search?q=over...SogLIRhsFRBN1M

My old kitchen had the typical hood above with a light and exhaust fan. Almost all new kitchens in the US that Iíve seen now have the over range microwaves instead. But youíve eliminated the range hood, but you still need the light and fan. Those are built into the underside of the microwave.

In an apartment like mine, in addition to clearing odors you can use the fan to assist with the air flow. The apartment footprint is rectangular, with all the windows and radiators and AC units located on one of the short ends of the rectangle.

The kitchen is on the other short end of the rectangle. So sometimes I run the fan, even when Iím not cooking, to increase general ventilation.
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Old 08-15-2019, 01:00 PM
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Originally Posted by Ann Hedonia View Post
The resolution is that they found a way to vent by going through the ceiling. This will connect to the ďbuilding ventilation systemĒ, as it were.
And that is almost certainly a code violation. Domestic kitchen exhaust equipment duct systems need to be independent of other exhaust systems. Beyond the issue of transferring odors to other parts of the building, the main issue is collection of grease that is a fire hazard. Sorry, but this should be corrected.
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Old 08-15-2019, 01:15 PM
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Although the building exhaust system you describe doesn't actually have ducts but uses spaces between walls and ceilings, I still consider this a code violation. Rather than ducts, what the building exhaust system uses is what is technically called a plenum, and no fire inspector would allow a kitchen hood exhaust into such a plenum.
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Old 08-15-2019, 01:31 PM
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Quote:
Originally Posted by Alessan View Post
I'm with Nava - I have a hard time visualizing the situation. How high is the microwave above the stove?
If I'm understanding it correctly it's a microwave-hood combo. So what actually needs venting is neither the stove nor the microwave: it's the hood.
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Old 08-15-2019, 05:02 PM
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Quote:
Originally Posted by Dag Otto View Post
Although the building exhaust system you describe doesn't actually have ducts but uses spaces between walls and ceilings, I still consider this a code violation. Rather than ducts, what the building exhaust system uses is what is technically called a plenum, and no fire inspector would allow a kitchen hood exhaust into such a plenum.
I will certainly look into this. It is also possible that I misunderstood what they did.
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