# OTR Microwave back wall venting?



## rmoore1 (May 25, 2015)

I'm getting ready to replace a microwave (that is currently set up to only recirculate the air) and I can tell there was an old range hood installed prior to that. It had to have been venting through the back of the wall (not roof venting) b/c the cabinet above the current microwave has no signs of any venting and I see a vent exhaust cap outside on the side of the house near the kitchen window (it says Jenn-air).

My question is when I get that old microwave down to install the new one, what are the odds my new microwave (its a GE JVM3160RFSS) back venting damper assembly will match up with the old range hood duct? Are those usually pretty standard sizes? The new microwave venting damper is made to join to 3 1/4 x 10" ductwork. Or, am I in for a huge headache?

We cook A LOT and i'm tired of just recirculating everything.


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## SPS-1 (Oct 21, 2008)

We are all just guessing. Take down the microwave and then you know what you got. 
You might have to do a little retrofitting. If you have an existing vent back there that is accurately on center, that's 90 percent of the battle.


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## hardwareman (Oct 9, 2010)

slim to none


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## rmoore1 (May 25, 2015)

hardwareman said:


> slim to none


Well, the good news is that the existing venting ductwork was pretty much exactly where I needed it to be. The bad news is that it goes about 3 inches before taking a 90 degree turn up (and down?) to take it out of the house. So, its almost like venting right into a wall which weakens the power of the vent severely. But, to me, i still like it better than venting grease and steam right back into the room (and directly onto the cabinets above).


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## Ron6519 (Mar 28, 2007)

Anything stopping you from rerouting the vent to directly exit the building?


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## rmoore1 (May 25, 2015)

Kind of. The garage is directly behind that wall. 

I think the best bet would be to change the way the microwave vents to be out the top, instead of the rear. Then, add some duct work to go right into the cabinet above and meet up with the existing duct work somewhere. But, that's above my current level of skill.


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## Ron6519 (Mar 28, 2007)

rmoore1 said:


> Then, add some duct work to go right into the cabinet above and meet up with the existing duct work somewhere. But, that's above my current level of skill.


What do you mean, "existing ductwork"? A microwave exhaust is that, a microwave exhaust. You can't add it to anything.
You can add ductwork that gets it to the exterior if the length of ductwork is less then the manufacturers stated maximum length. This also has some. "small print". Every 90 degree turn equals about 5 linear feet.
So a 10 foot straight run plus 3- 90 degree turns equals 25 feet.


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