# Tight space duct work (7" duct for microwave venting) - is this possible?



## Nealtw (Jun 22, 2017)

Flexible duct and the crimped end goes in the wall. 

https://www.wayfair.ca/BuildersBest...MI25XBmtat6QIVCx-tBh0DRQfFEAQYASABEgI_OPD_BwE


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## jplee3 (Jan 11, 2012)

Nealtw said:


> Flexible duct and the crimped end goes in the wall.
> 
> https://www.wayfair.ca/BuildersBest...MI25XBmtat6QIVCx-tBh0DRQfFEAQYASABEgI_OPD_BwE



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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## Nealtw (Jun 22, 2017)

jplee3 said:


> 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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## Bud9051 (Nov 11, 2015)

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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## SPS-1 (Oct 21, 2008)

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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## jplee3 (Jan 11, 2012)

Bud9051 said:


> 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.
> 
> ...



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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## Bud9051 (Nov 11, 2015)

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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## jplee3 (Jan 11, 2012)

Bud9051 said:


> 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.
> 
> ...


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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## jplee3 (Jan 11, 2012)

Okay I contacted one place and they want to charge $300 to fabricate something... guess I'll have to call around. Or suck it up and try to 'force-fit' something together


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## Nealtw (Jun 22, 2017)

You might have a chance if you can find a tight 90 and a tight 45


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## jplee3 (Jan 11, 2012)

Nealtw said:


> 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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## SPS-1 (Oct 21, 2008)

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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## Nealtw (Jun 22, 2017)

jplee3 said:


> 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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## jplee3 (Jan 11, 2012)

Nealtw said:


> 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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## Bud9051 (Nov 11, 2015)

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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## Nealtw (Jun 22, 2017)

www.southwarkmetal.com/product/45-flat-stack-angle-broadway-longway/


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## jplee3 (Jan 11, 2012)

Bud9051 said:


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



It's actually an over range microwave exhaust - there was a range hood previously and I removed that to put this over range microwave up.


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## Nealtw (Jun 22, 2017)

jplee3 said:


> 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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## jplee3 (Jan 11, 2012)

Nealtw said:


> www.southwarkmetal.com/product/45-flat-stack-angle-broadway-longway/


This is a good idea too - just not sure about the dimensions and fit. It may end up going too long. Will have to look at the dimensions on these but it doesn't say the height of the 45-degree one


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## Nealtw (Jun 22, 2017)

jplee3 said:


> This is a good idea too - just not sure about the dimensions and fit. It may end up going too long. Will have to look at the dimensions on these but it doesn't say the height of the 45-degree one


You would have to cut the wings off anyway but you could cut it almost anywhere to fit.


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## jplee3 (Jan 11, 2012)

Nealtw said:


> jplee3 said:
> 
> 
> > This is a good idea too - just not sure about the dimensions and fit. It may end up going too long. Will have to look at the dimensions on these but it doesn't say the height of the 45-degree one
> ...



Ahh ok. On that note what would the best type of snips or sheet metal shears be for making these cuts as well as 'standard' sheet metal cuts
like if I just wanted to cut snap lock sheet metal tubing whether straight or angled cuts? Any particular brands or specific snips ? I may stop by Lowe's later to grab a pair.


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## Nealtw (Jun 22, 2017)

jplee3 said:


> Ahh ok. On that note what would the best type of snips or sheet metal shears be for making these cuts as well as 'standard' sheet metal cuts
> like if I just wanted to cut snap lock sheet metal tubing whether straight or angled cuts? Any particular brands or specific snips ? I may stop by Lowe's later to grab a pair.



You don't want advice from me for that.:biggrin2:
You might start another thread with that question.


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## Nealtw (Jun 22, 2017)

jplee3 said:


> Ahh ok. On that note what would the best type of snips or sheet metal shears be for making these cuts as well as 'standard' sheet metal cuts
> like if I just wanted to cut snap lock sheet metal tubing whether straight or angled cuts? Any particular brands or specific snips ? I may stop by Lowe's later to grab a pair.


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## HotRodx10 (Aug 24, 2017)

Would a semi-rigid duct be better than the flex, or would it suffer from the same issues?


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## tom_poconos (Nov 6, 2017)

You'd be surprised what you can make easily yourself out of sheet metal with some snips, sheet metal screws and HVAC tape (the metal kind). What I do is draw the net of the custom object I need on paper and then cut it out. It's really just like what kids learn at school about prisms and cylinders but with metal.

If you have some spare sheet metal give it a go. You are so close to closing the duct, you just need another segment in there.


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## jplee3 (Jan 11, 2012)

tom_poconos said:


> You'd be surprised what you can make easily yourself out of sheet metal with some snips, sheet metal screws and HVAC tape (the metal kind). What I do is draw the net of the custom object I need on paper and then cut it out. It's really just like what kids learn at school about prisms and cylinders but with metal.
> 
> If you have some spare sheet metal give it a go. You are so close to closing the duct, you just need another segment in there.



I plan to pickup some snips. I was actually thinking about just reusing the snaplock tubing that was custom cut for the old range hood and trimming it down, slipping it inside the adjustable elbow, and use that to bridge the gap - this is basically what was done on the range but the taping job was awful. The duct is also filthy with old grease build-up and tape residue - is there a good way to clean those things btw? Soak in hot water and dishsoap? Simple green? GooGone? I applied some GooGone to take off the initial grease...


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## tom_poconos (Nov 6, 2017)

jplee3 said:


> The duct is also filthy with old grease build-up and tape residue - is there a good way to clean those things btw? Soak in hot water and dishsoap? Simple green? GooGone? I applied some GooGone to take off the initial grease...


If you're ok with nasty chemicals, Acetone or paint thinner will clean pretty much any gunk off metal.


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## jplee3 (Jan 11, 2012)

tom_poconos said:


> jplee3 said:
> 
> 
> > The duct is also filthy with old grease build-up and tape residue - is there a good way to clean those things btw? Soak in hot water and dishsoap? Simple green? GooGone? I applied some GooGone to take off the initial grease...
> ...


I have denatured alcohol too. Would that work?


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## jplee3 (Jan 11, 2012)

jplee3 said:


> I have denatured alcohol too. Would that work?



I ended up filling a 5gal bucket with water and squirting Dawn in and letting these things soak for a good hour, scrubbing them occasionally throughout. I was able to get probably 90% of the gunk off and they look much better. Next part is to go get the aviation shear set from Harbor Freight and cut down the current ducting to size.


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## jplee3 (Jan 11, 2012)

OK, so it's not pretty but here's what I came up with:


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I basically just reused the previous snaplock duct and cut it down several inches little by little then re-fit to the point where I was able to cram it into the adjustable elbow and finally slide it over the boot. I have it in place where I *could* just tape everything. There is a slight bit of overhang where the transition snaplock piece meets the top of the duct boot and a small leakage of air but not significant - am I going to want to address that? Perhaps by cutting a slot to conform that overhang and bend it down to fit against flush against the top side of the duct boot?



The other concern is with the back part of the duct boot:

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I think to do it *right* I would unbolt the microwave and tape down the boot in the back - it's really tempting to omit that step though and just cram some tape right down into that "slot" between the back of the duct and the wood strip lol. 

Should I just go ahead and tape the snaplock piece to the elbow as-is and also the part where it slips over the boot (so basically the elbow, transition and duct boot are taped together first). Then slowly unbolt the microwave to tilt back and tape all around? Then pop it back into place and get it up to the outlet and be done? Or is there an 'easier' way or order to follow to get to the finish line?

Should I grab some of this stuff to try to fill any gaps where there's air leakage? 
https://www.lowes.com/pd/Design-Polymerics-64-fl-oz-Gray-Duct-Sealant/3736193
Or is the aluminum foil tape going to be sufficient for all that?


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## HotRodx10 (Aug 24, 2017)

It looks like a pretty good fit to me. A couple of wraps of aluminum foil tape, and it should be ready for action.


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## jplee3 (Jan 11, 2012)

HotRodx10 said:


> It looks like a pretty good fit to me. A couple of wraps of aluminum foil tape, and it should be ready for action.



I agree. I'm inclined towards unbolting the MW so I can tape the back part of the duct boot down as much of a PITA as that sounds. But it sounds like I should probably tape the joints/connections I've already made higher up before I do that? Or another idea that crossed my mind is to use a sharpie and mark the positions of the pieces so I know where to adjust them back to once I've taped the boot down.


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## HotRodx10 (Aug 24, 2017)

> I'm inclined towards unbolting the MW so I can tape the back part of the duct boot down as much of a PITA as that sounds.



I would try slipping a couple 8" or so pieces of unrolled and uncovered tape down behind the boot and then just pulling them around, before dropping the MW.


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## jplee3 (Jan 11, 2012)

HotRodx10 said:


> I would try slipping a couple 8" or so pieces of unrolled and uncovered tape down behind the boot and then just pulling them around, before dropping the MW.


Good idea - the foil tape has the plastic backing on it to where I could potentially do that then just pull the backing off once I have it positioned I think. Maybe I'll try that to see if I can do it. It'll still be super tight but we'll see....

EDIT: I just tried and I think it's just too tight of a squeeze, unfortunately. Since everything is off at this point I might as well just unbolt it to tilt back and tape. :T


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## HotRodx10 (Aug 24, 2017)

What worked for me was peeling the backing a little less than halfway, and folding it back, so that I have the bare end of the tape in one hand and the peeled end of the backing and the unpeeled end of the tape in the other. Once it's in position, I can peel the backing the rest of the way, since it's already on the correct side to do it.


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## jplee3 (Jan 11, 2012)

HotRodx10 said:


> What worked for me was peeling the backing a little less than halfway, and folding it back, so that I have the bare end of the tape in one hand and the peeled end of the backing and the unpeeled end of the tape in the other. Once it's in position, I can peel the backing the rest of the way, since it's already on the correct side to do it.


Yea, that's what I was trying to do - I was just unable to slide the tape into the crevice at the right angle because it's so close to the wall and also with the supporting cleat almost in the way - it's like an "L"
It would be really hard getting the tape pressed on fully in the back too for the best seal since I have no way to running my finger or anything over the tape to close any gaps, etc.



















To get a good connection in the back (when I initially taped it on, I had to get the tape attached to the top back edge of the microwave then onto the damper vent adapter and duct boot (which slips over that piece). If I were to stick the tape down as shown in the pic, it wouldn't really secure the back or close any 'gap' 
I guess what I *should* have considered doing was your suggestion of taping half of it down to the upper-back part where I needed to and leaving the plastic peel on the other half and doing this BEFORE putting the microwave up. Then it would have been in place and I wouldn't be in this situation 

Anyway, I'm pretty sure I'll need to just unbolt it at this point


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## HotRodx10 (Aug 24, 2017)

Bummer! Ah well, that's how it goes with projects like this - you always know at the end how you should have done it.


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## jplee3 (Jan 11, 2012)

Well, I got it taped and it looks like it's good to go as far as I can tell.

Not super pretty but seems functional LOL:



























Quick question though: I noticed at the rotation joints there's a slight 'draft' - am I going to want to tape those joints all around? Or should I just leave those alone?


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## Nealtw (Jun 22, 2017)

jplee3 said:


> Well, I got it taped and it looks like it's good to go as far as I can tell.
> 
> Not super pretty but seems functional LOL:
> 
> ...


 Tape them too.
It looks great, good job. :biggrin2:


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