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GMX 08-25-2012 09:46 PM

Exhausting an OTR microwave
Hello, just purchased a new Samsung OTR microwave to replace an ancient, dead GE Spacemaker which was set up for rear exhaust.

I'd like to also use rear exhaust on the new one, however when we pulled the old one off the wall, we found that the builders/installers (we're not the original homeowners) installed the exhaust duct offset about an inch to the side of where it should be (sigh...). The result is that the microwave will exhaust partly into the wall structure.

I don't see an easy way to fix this, other than completely re-doing the exhaust ductwork and the siding on the house. This is not an option right now.

So now I'm considering doing front exhaust (recirc into kitchen thru filter) on this thing. It does have a charcoal filter, but I'm wondering, how much filth will this contribute to the innards of the microwave over the years? Other than changing the filters, will it get disgusting and need to be periodically cleaned out?

Any other pros/cons to doing front/recirc vs. rear exhaust?

Also, does anyone know of any tricks to deal with the offset ductwork issue so that we could still use rear exhaust? I was thinking of blocking off the offset part but of course that would reduce the overall exhaust area by a good 10-15%, and could still end up leading to grease and crud buildup on the block-off plate, tape, or whatever I use to cover it.

notmrjohn 08-26-2012 03:05 PM

I think your "block head'...err... block off idea would work. I did the same connecting AC to plenum, course I wasn't dealing with grease and such. Don't forget to block off the other side of duct. But how was the offset dealt with in old unit? On to the wall? If the ducts are rectangular, you could make the edge of the blocker towards the Micro-wave at an angle leading into duct instead of just a right angle. Mebbee that wouldn't collect as much grunge. Like this l \l l/ l looking down on it with micro at bottom of my 'drawing.' Round duct would be harder.
I'm not a big fan (hah) of recirculating hoods, the charcoal filters don't remove every odor and they need replacing every so often. They don't remove as much moisture either. I think you're off on that reduction of 10%, it may be that in area but not that much in air movement. that stuff gets tricky, ya want the right air volume at the right velocity and ya got equivelant ducting with different areas and elbows and sometimes it blows and sometimes it sucks. Like when its just an inch off and ya gotta vent your anger somewhere.

joecaption 08-26-2012 04:44 PM

A micro wave is going to be dealing with moisture not grease.
When the last time you cooked meat in a microwave?

hvac122 08-26-2012 06:16 PM

It also exhausts the range. The filters are right above the range so it could be grease.
Post a picture of the venting so we can give you ideas on how to vent.

Its A Good Life!

hardwareman 08-26-2012 07:23 PM

yeah, microwaves are full of grease. Doesn't matter if they are vented to the outside or inside. If your cooking on the stove and running the fan it will pull lots of grease into the unit, thats just the way it is

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