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Discussion Starter · #1 ·
Hey guys,

Looking for some help on venting duct work for a microwave. I previously had a range hood in place that I removed and replaced with an over range microwave. My intention was to reuse the 7" pre-existing ductwork. However, it has proved quite cumbersome to work with. Now I'm not even sure if it will work.





The 7" will just not reach over - there was another section of 7" duct that I pulled out but it's big (the vent was lower profile so more room to work with the ducts). And I don't have any sheet metal shears to cut this stuff :(

Is there a way I can force it in to work or retrofit? If not, am I going to need to size down to smaller ducting? I'm not sure if there's a certain minimum requirement diameter for duct work in my area (Orange County, CA) if that's a factor.

This is my first over range microwave install let alone duct work, so I'm in a dark (outside of these forums and youtube lol)
 

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Discussion Starter · #3 · (Edited)

Thanks Neal! I've heard flex ducts aren't usually recommended for most microwave installs due to the amount of build-up that can occur in the creases, etc unless the technology has changed? Also, I've also heard some municipalities/counties/etc only allow rigid ducting and nothing else. I'm not sure what my area's requirements are but I haven't been able to find any specifics on the matter (this is in Irvine, CA to be specific)

EDIT: I just clicked on the link and it redirected to https://www.houzz.com/discussions/3405083/otr-microwave-flex-vent where they have an at-length discussion of the topic on using rigid vs flex venting. Looks like the resolution for her was that she needed to switch to rigid:
"Good news. It looks like contractor just found a solution. He was calling back & forth w/ worker for exact measurements, etc, and I believe contractor was at Home Depot looking at options. Seems he found some kind of elbow(s) and rigid duct pieces that will work using the current outdoor vent hole. I am soooo relieved! Thank you all so much for your help & support! So grateful!"
 

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retired framer
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Thanks Neal! I've heard flex ducts aren't usually recommended for most microwave installs due to the amount of build-up that can occur in the creases, etc unless the technology has changed? Also, I've also heard some municipalities/counties/etc only allow rigid ducting and nothing else. I'm not sure what my area's requirements are but I haven't been able to find any specifics on the matter (this is in Irvine, CA to be specific)

EDIT: I just clicked on the link and it redirected to https://www.houzz.com/discussions/3405083/otr-microwave-flex-vent where they have an at-length discussion of the topic on using rigid vs flex venting. Looks like the resolution for her was that she needed to switch to rigid:
"Good news. It looks like contractor just found a solution. He was calling back & forth w/ worker for exact measurements, etc, and I believe contractor was at Home Depot looking at options. Seems he found some kind of elbow(s) and rigid duct pieces that will work using the current outdoor vent hole. I am soooo relieved! Thank you all so much for your help & support! So grateful!"
Good luck :wink2:
 

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Definitely, a custom made adapter can be made to fit what you have. Not an off the shelf solution, but there is plenty of room.

Here is an initial thought. Assuming that galvanized elbow is removable leaving a hole in the wall. Then you have a hole to the left of the duct pointing up from the microwave.

Picture a straight duct pointing up from the mw and another straight down from the exhaust duct. Connect the two with a box closing tops and bottoms and providing deflectors to steer the airflow. Provide a removable cover for cleaning.

I would start by building something out of poster board and tape. Pop rivets and foil tape could probably be used to assemble it.

If you can't do the diy, make a mock up and take it to a sheet metal shop and they can certainly make something for you.

Bud

Just searched and here is a straight up to right angle example, obviously too long but close to what I was trying to explain.
https://www.amazon.com/Dundas-Jafine-UD48S-Straight-Outlet/dp/B001AH3K72?ref_=fsclp_pl_dp_2
 
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I am thinking like Bud. If you can't move that duct, somebody will be making a custom fitting for that. Either you, or a pro.

I would be making it myself. If you don't have the tools, make a rigid template of the sizes and locations of the openings, so the sheet metal shop does not need to come out and measure and fit the pieces.
 

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Discussion Starter · #7 ·
Definitely, a custom made adapter can be made to fit what you have. Not an off the shelf solution, but there is plenty of room.

Here is an initial thought. Assuming that galvanized elbow is removable leaving a hole in the wall. Then you have a hole to the left of the duct pointing up from the microwave.

Picture a straight duct pointing up from the mw and another straight down from the exhaust duct. Connect the two with a box closing tops and bottoms and providing deflectors to steer the airflow. Provide a removable cover for cleaning.

I would start by building something out of poster board and tape. Pop rivets and foil tape could probably be used to assemble it.

If you can't do the diy, make a mock up and take it to a sheet metal shop and they can certainly make something for you.

Bud

Just searched and here is a straight up to right angle example, obviously too long but close to what I was trying to explain.
https://www.amazon.com/Dundas-Jafine-UD48S-Straight-Outlet/dp/B001AH3K72?ref_=fsclp_pl_dp_2

Haha, a lot of this is over my head in terms of even making a mock-up of such a thing!

The link you posted does look like a good solution though - it's too bad those are intended for dryer ventilation only. The amount of space between the top of the boot to the opening in the wall is definitely less than a foot of space and there is maybe 1-2" of space from the wall where the duct boot opening sits.

I wonder if a 45" adapter would complete the transition as is. A 7" 45-degree adapter would be tight and I'd have to snip or use pliers to cram the thing in to the duct boot and the existing 90-degree adjustable... what about a 6" 45-degree adapter though? Or would that be way too small and slip through?
 

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First question, do you have a sheet metal shop in your area? All forced air systems, heating or cooling, need ducts and either they make their own or they have a shop make them. Take your pictures (and face mask) to a ss shop and talk to them. I have run into some really nice business people in my life and you might find one of them to walk you through it.

What you see as a problem might be their opportunity to have a feel good day by helping.

I've been on both sides of that opportunity and it does feel good.

Bud
 

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Discussion Starter · #9 · (Edited)
First question, do you have a sheet metal shop in your area? All forced air systems, heating or cooling, need ducts and either they make their own or they have a shop make them. Take your pictures (and face mask) to a ss shop and talk to them. I have run into some really nice business people in my life and you might find one of them to walk you through it.

What you see as a problem might be their opportunity to have a feel good day by helping.

I've been on both sides of that opportunity and it does feel good.

Bud
Good question - I can Google but Google isn't always 100% accurate either. Is there some sort of 'directory' I can reference? Or perhaps a more specific search term other than "sheet metal shops" I can search with to determine if there's a place nearby that might help? Maybe an HVAC company?

The other thing is with the measurements and angles - if I am unable to make a template, let alone, an accurate one, I'm not sure how I would convey the necessary dimensions if I were just to call them up or walk in and have them produce something. I think I've found at least a couple shops in the area though...
 

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Discussion Starter · #12 ·
You might have a chance if you can find a tight 90 and a tight 45

Yea, I started hunting around for one of those super tight 90-degree turns. Not sure if they make any of the 7" variety (most of those close elbows look to be 4" for dryer vents) but will keep looking I suppose. I actually crammed the old fitting into the 90-degree elbow and if I were to get a pair of tin snips, I might be able to cut it down to the right size. It's just awkward fitting it in that space.

 

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One thing that might help you get something made is if you remove the existing duct on the top of the microwave and take it to an HVAC shop. And then tell them you want "a new fitting, something like this, but with the 7" outlet shifted x.xx inches to the left, and y.yy inches higher" I think you would need to accept that you will need to cut the bottom of the cabinet a little bigger --- the shop could make something that goes around that cabinet bottom, but the more specifications you give them, the more they figure they will be making it three times before you are satisfied --- and price the job accordingly. Maybe have them leave out the mounting holes to microwave so you can do a bit of fine adjustment.

I know you won't look forward to pulling off and reinstalling that microwave.
 

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Yea, I started hunting around for one of those super tight 90-degree turns. Not sure if they make any of the 7" variety (most of those close elbows look to be 4" for dryer vents) but will keep looking I suppose. I actually crammed the old fitting into the 90-degree elbow and if I were to get a pair of tin snips, I might be able to cut it down to the right size. It's just awkward fitting it in that space.
6" is what is required, you could change your take off boot and buy or make a flat adapter for the wall. But not sure how much more room that gives you.
 

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Discussion Starter · #15 ·
6" is what is required, you could change your take off boot and buy or make a flat adapter for the wall. But not sure how much more room that gives you.
It may offer a bit more flexibility. But at this rate if I put a step-down adapter from the wall, I think it may come out a bit too far - the duct boot from the microwave is very close to the back wall as it is.
 

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Is this an exhaust fan over a kitchen range rather than a microwave exhaust? Is it essentially a range hood?

Bud
 

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It may offer a bit more flexibility. But at this rate if I put a step-down adapter from the wall, I think it may come out a bit too far - the duct boot from the microwave is very close to the back wall as it is.
Not if you cut a 6" hole i a 7" plug. :smile:
 
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