Microwave installation - venting

rutledj · 10-26-2012, 03:23 PM

I'm remodeling my kitchen and installing a new microwave above the cooktop. It will be vented straight out the back wall and then 90 degree up through the garage roof.

I'm having a hard time understanding how to connect the adapter that came with the microwave (the small piece that has the flap in it. It says in the instructions to connect a 3 1/4 x 10 rectagular to 6" round vent to adapter.
Problem is the two units don't form a tight fit (maybe they aren't supposed to?).

Do I use duct tape to connect them and create a good seal? This will be difficult to do since the adapter fits onto the back of the microwave and the pipe sticks through the sheetrock (flush with it I would assume). I don't see any way to get back there to tape it.

Any suggestions?

Attached are a few pics of the two items.

Thanks,
Rut

funfool · 10-26-2012, 04:23 PM

I hate venting through the back, can be done.
As you see, typically the piece in the first pic is to be installed before hanging the microwave. This almost makes it impossible without cutting a huge hole behind the oven first, Just so when you swing the oven up into place the piece will clear.
This will be covered by the back of the oven, but no way to repair the drywall.
In one new home, had the hvac guys install the duct work during rough in.
Only need to be 1/4" off on rough in and is a problem.
Anytime I exhausted out the back, even though it is an option, has always ended in a compromised situation.

If possible, I would suggest going through the top of the cabinet, then 90 out to the garage and 90 up.
More 90's you add the more restriction you get in air flow.

Assuming have drywall in the garage, you could cut a larger hole then needed for room to work, mark and locate the hole for oven and cut it out from the garage side, get the duct through the wall, then patch the larger hole in the garage.
Would like to hand you a easy button, I do not see it in this case.

rutledj · 10-26-2012, 04:28 PM

Well for now I have the drywall taken down on the inside so I could mount it (assuming I could get it aligned up correctly the first time). On the garage side I have one layer of osb and another of t-111 so going at it from that direction would be worse.

funfool · 10-26-2012, 05:08 PM

Well this should not be to hard if drywall is off in the kitchen.
You could dry fit it and mark the location of where the venting will be and cut the hole and install it.

Oh wait! We have a order to do things, is nice to have the drywall finished before hanging cabinets.
I feel your pain here, not trying to be a smart alec.
You can imagine if you dry fit it now, then drywall then hang cabinets, it would take a very small variance and it would not line up.
Is impossible to get your hands behind the oven to help it line up.

I really think that exhausting out of the rear of the microwave should only be used as a last resort. Yes it is a option, just one option I would run from.

Others may have better ideas, I would avoid going out the back if through the top is a option.