# Venting an oven range microwave



## Plumber101 (Feb 25, 2009)

For a range microwave a 4" pipe will be fine. 

Look at the instructions provided for how to connect.


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## DannyT (Mar 23, 2011)

check the requirements of the microwave. i just redid our kitchen and ran a 6 inch line for the vent hood as per the microwave installation instructions.


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## how (Feb 26, 2011)

I am assuming that this is a fan assist vent? If not, maybe you should tell us where this vent goes & exits?
While 6 " makes for a quieter fan operation, 4" is better than nothing and the requirements for venting a microwave range isn't that high.


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## demandrew (Dec 9, 2011)

how said:


> I am assuming that this is a fan assist vent? If not, maybe you should tell us where this vent goes & exits?
> While 6 " makes for a quieter fan operation, 4" is better than nothing and the requirements for venting a microwave range isn't that high.



The vent would go from the back of the microwave through my brick wall and outside.

I'm tending to agree with the better than nothing appraisal.

Thanks for all the help


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## joecaption (Nov 30, 2011)

I've installed at least 20 wall mount microwaves and not one had an outside vent. And 0 complants from customers.


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## sktn77a (May 11, 2009)

If the microwave is going to vent the main cooking range below it, I would stick with a regular range vent and use a built in or countertop microwave. The vent fans in over-the-range microwave ovens are worthless.


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## hvac122 (Dec 10, 2007)

If your talking about a micro hood microwave (fits above range with a vent fan inside) these are most often rated at 300 CFM and require a 6" or a 3 1/4 x 10" vent to the outside. They work fine for venting.


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## demandrew (Dec 9, 2011)

hvac122 said:


> If your talking about a micro hood microwave (fits above range with a vent fan inside) these are most often rated at 300 CFM and require a 6" or a 3 1/4 x 10" vent to the outside. They work fine for venting.


I think this is the kind of microwave I'll be getting. I have a 3 1/4 x 10" vent but i would only be able to pass it through a 4" pipe to the outside. I know that they often require higher but I'm wondering if this 4" will just squeeze by and at the very least be better than not venting at all.


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## hvac122 (Dec 10, 2007)

It may work or may not. Could overheat and overwork the motor and will be louder.


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## DannyT (Mar 23, 2011)

but it will be better than nothing at all.


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## demandrew (Dec 9, 2011)

Thanks for the tips. I may just have to make do with the 4inches and consider it better than nothing as I'm not sure how comfortable I am enlarging the hole through my brick wall - unless some of you can convince me that it's a relatively easy and stress free job!


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## bob22 (May 28, 2008)

I'm not sure how easy it will be to convert from the square 31/4" x 10" opening in the microwave to a 4" round in 31/2" or so? Is there a transition fitting made to do this readily available?


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## ben's plumbing (Oct 6, 2011)

I really don't like that better or nothing thougth....4" is to small ..as mentioned 3 1/4 x 10 or 6" round....is what is required... anything less is anybody's guess......how about code....


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## ben's plumbing (Oct 6, 2011)

bob22 said:


> I'm not sure how easy it will be to convert from the square 31/4" x 10" opening in the microwave to a 4" round in 31/2" or so? Is there a transition fitting made to do this readily available?


 no because it won't work...well not right anyway...:no:


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## oh'mike (Sep 18, 2009)

Get a 4" angle grinder and a diamond blade---cut the brick---it is a bit of work,but it's the right way--

That machine needs either 6" round or 3 1/4 x 10 to function properly--Post pictures--we will help from our desk chairs.

Right is right--4" is wrong---


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## demandrew (Dec 9, 2011)

oh'mike said:


> Get a 4" angle grinder and a diamond blade---cut the brick---it is a bit of work,but it's the right way--
> 
> That machine needs either 6" round or 3 1/4 x 10 to function properly--Post pictures--we will help from our desk chairs.
> 
> Right is right--4" is wrong---


I am feeling more ambitious so I might give it a go. No angle grinder but I have a decent masonry bit that might help me out. Could I succeed by drilling a few holes around the perimeter of the enlarged 6" space and then chisel?

The thing is, "the man at the big box store" gave me the 3 1/4 x 10 piece, which is rectangular at the opening to attach to the microwave, and then funnels into a round pipe that more or less fits around a 4" . Is this not what a 3 1/4 x 10 is supposed to look like? There were a few different variations depending on what direction you want to take things, my piece turns down immediately and the way I left it last there was just enough room within the wall (i have 4.5inches) to send it back from the microwave, down (I have to send it down my wall a bit because the old hole is too low) and then out the wall. Does any of this make sense?

I'll try to add more pictures tomorrow morning to help clarify. Thanks for the help, you guys are great.


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## oh'mike (Sep 18, 2009)

Look at the 3 1/4" x 10 outside vent covers---it just might be that removing a brick completely might be easier than making a 6" round hole--

Weigh the options before you decide--

And yes--a hammer drill and a masonry bit will get the job done,also.


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## mpnret (Nov 11, 2010)

DannyT said:


> but it will be better than nothing at all.


Not really, because nothing at all is not an option. The vent is designed to flow a certain amount of air. It either pushes that air outside through a proper sized vent or inside through a vent at the top and back into the room. Selecting the outside option then then restricting the flow of air with a undersized vent is not a good idea.


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## demandrew (Dec 9, 2011)

ok folks. Here are some photos to help this thread along.

Here's my original hole:

http://www.diychatroom.com/members/...y-kitchen-vent/5162-photo-2012-03-01-11-17-2/

Here's what it looks like after pulling out some of the surrounding insulation. It seems I may already have some wiggle room to add a larger pipe:

http://www.diychatroom.com/members/.../my-kitchen-vent/5163-photo-2012-03-01-11-18/

Originally, I was going to add something like this:

http://www.diychatroom.com/members/.../my-kitchen-vent/5164-photo-2012-03-01-11-21/

And then something like this:

http://www.diychatroom.com/members/.../my-kitchen-vent/5165-photo-2012-03-01-11-22/

Thoughts? Concerns?

P.S. How do I post photos directly in a post? Do I always need to create an album first?


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## bob22 (May 28, 2008)

Demandrew: see: http://www.diychatroom.com/f19/how-attach-photo-post-12559/


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## demandrew (Dec 9, 2011)

bob22 said:


> Demandrew: see: http://www.diychatroom.com/f19/how-attach-photo-post-12559/


Thank you kindly.


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## demandrew (Dec 9, 2011)

So there's been a new development.

Thanks to everyone's enthusiasm and encouragement here, I've decided to take the plunge and replace my old 4" round with a new 3 1/4 x 10" exhaust vent. Exciting times.

So now I'm getting ready to convert by 4" or so round hole to the appropriate rectangular hole. Any tips for how to achieve this switch? I'm planning on orienting my new rectangle hole such that the old circle sits in the bottom right corner, or I guess just the right side. I thought I might drill some holes through at the corners of my rectangle, maybe a few more around the perimeter (I'm using a 3/4" bit) and then...and then chisel? Not too sure here. Any tips?


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## COLDIRON (Mar 15, 2009)

By the looks of the square to round I think your on to something, the out put of micro wave exhaust fan should flow through that 4" round OK.
If it were mine I would do just what you did without disturbing the outside of the house. If you can line up that 31/4 x 10 with the back of the micro wave exhaust I think you got it made. There are millions of microwaves installed with just a recirculating system that takes no exhaust outside, so you are ahead of the game if you can make that ductwork arraignment work.
Another option is to seal up the exhaust hole before you install the micro wave and just reset the fan to recirculate like many others.

I prefer to exhaust the air. Go for it don't mess with the outside of the house if you don't have to.


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## COLDIRON (Mar 15, 2009)

DannyT said:


> but it will be better than nothing at all.


I second that, 4"0 will vent fine.


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## ben's plumbing (Oct 6, 2011)

sorry guys I respectfully disagree....have a good day...:no:


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## oh'mike (Sep 18, 2009)

Where in the world is reducing a 3 1/4 x 10 down to 4" an acceptable air flow?

Is the inside opened up to expose the framing yet?


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## COLDIRON (Mar 15, 2009)

oh'mike said:


> Where in the world is reducing a 3 1/4 x 10 down to 4" an acceptable air flow?
> 
> Is the inside opened up to expose the framing yet?


Yes checkout his pictures, let me check my ductalater.

We're not talking heating and cooling here we're talking just exhausting a little smell and steam from cooking, don't have to maintain temperatures and humidity and how many microwaves are vented with just recirculating rather than exhaust ? They do absolutely nothing.


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## demandrew (Dec 9, 2011)

I see there's some disagreement here..
Well I'm gonna make a decision soon, but as of last night I was expecting to start breaking more of my wall away to allow for a straight 3 1/4 X 10.

Any tips on the best way to go about this/what's involved so I know better how to weigh my options?


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## bob22 (May 28, 2008)

Demandrew: Google how to cut a hole in a brick wall on you tube. Lots of videos there; look at a bunch to get the one you like best.
I saw someone on tv cut a hole; they predrilled a circular outline with a drill bit and then used a chisel to connect the dots.
I'm sure there are many ways to do it.


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## mpnret (Nov 11, 2010)

COLDIRON said:


> Yes checkout his pictures, let me check my ductalater.
> 
> We're not talking heating and cooling here we're talking just exhausting a little smell and steam from cooking, don't have to maintain temperatures and humidity and how many microwaves are vented with just recirculating rather than exhaust ? They do absolutely nothing.


Wrong and wrong. Above the range microwaves sit fairly close to the cooktop compared to range hoods. They are able to maintain this reduced clearance by by being capable of moving a certain amount of heat when things get going on the cooktop. Doesn't matter if you vent that heat outside or if you use the recirc option and vent it out into the room away from the cooktop, you are still moving a prescribed amount of heat from a critical area. These microwaves even have a overide thermostat that turns on the fan automatically when things get hot just in case you forget.


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## hvac122 (Dec 10, 2007)

mpnret said:


> Wrong and wrong. Above the range microwaves sit fairly close to the cooktop compared to range hoods. They are able to maintain this reduced clearance by by being capable of moving a certain amount of heat when things get going on the cooktop. Doesn't matter if you vent that heat outside or if you use the recirc option and vent it out into the room away from the cooktop, you are still moving a prescribed amount of heat from a critical area. These microwaves even have a overide thermostat that turns on the fan automatically when things get hot just in case you forget.


I agree. These are designed to move approximately 300 CFM either way.


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## Canucker (May 5, 2011)

How many cfm does the range move? If its much more than 250, 4" won't work very well. Can you still do it? Sure. But you're going to have some blowback because the vent isn't capable of exhausting as much as it flows, plus the added noise and wear on the fan, as hvac122 pointed out. If it were me, and the wall is open, cut out the brick and install a proper sized exhaust. Its not going to be easier to do it later


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## demandrew (Dec 9, 2011)

I guess the nature of these forums is that you have to work your way through varying opinions. But I think I like the sound of the last few comments the best.

I'm going to break open my wall a bit more to allow room for a proper sized vent. It will also let me move the mircowave slightly to the left which is a bonus. And I also want to learn how to do it, so why not take the opportunity and then be content to know that it's all vented properly.

Thanks for all the advice. I'll post some pics when it's all done!


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## oh'mike (Sep 18, 2009)

No one will criticize your work if you do it right---Keep us posted---you will be fine---


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## ben's plumbing (Oct 6, 2011)

demandrew said:


> I guess the nature of these forums is that you have to work your way through varying opinions. But I think I like the sound of the last few comments the best.
> 
> I'm going to break open my wall a bit more to allow room for a proper sized vent. It will also let me move the mircowave slightly to the left which is a bonus. And I also want to learn how to do it, so why not take the opportunity and then be content to know that it's all vented properly.
> 
> Thanks for all the advice. I'll post some pics when it's all done!


 yes opinions vary..buy doing it right is truly the best option there is...as mike said keep us posted...:yes:


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## COLDIRON (Mar 15, 2009)

demandrew said:


> I think this is the kind of microwave I'll be getting. I have a 3 1/4 x 10" vent but i would only be able to pass it through a 4" pipe to the outside. I know that they often require higher but I'm wondering if this 4" will just squeeze by and at the very least be better than not venting at all.


The answer to your question is Yes.:yes:


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## demandrew (Dec 9, 2011)

Thanks again for everyone's input. There have been interesting developments. I ended up putting in a new 3 1/4 x 10" vent. It was a pretty daunting task at first, but I managed my way through it. 

If you care to take a look you can read about it in my ongoing project showcase: http://www.diychatroom.com/f49/my-f...ation-mixed-ikea-exposed-brick-135811/index2/ 
Take a look at the whole showcase if you like, and feel free to leave feedback, but the vent specific posts begin towards the end of page 2.

If you want to avoid any reading you can also just look at the photos here:
http://www.diychatroom.com/members/demandrew-135957/albums/my-kitchen-vent/


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## 12penny (Nov 21, 2008)

Be proud...nice job.


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## bob22 (May 28, 2008)

Well done! Looks good. Time to go into the business I guess.


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## demandrew (Dec 9, 2011)

12penny said:


> Be proud...nice job.





bob22 said:


> Well done! Looks good. Time to go into the business I guess.



Thanks for the kind words! Not sure if I'm ready for the business just yet, but thanks for the encouragement.


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## ben's plumbing (Oct 6, 2011)

demandrew said:


> Thanks for the kind words! Not sure if I'm ready for the business just yet, but thanks for the encouragement.


 really nice job...how high up is that?


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## COLDIRON (Mar 15, 2009)

Looking Good just like a Pro did it.


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## demandrew (Dec 9, 2011)

ben's plumbing said:


> really nice job...how high up is that?


Hey thanks. I would say it's about 20' up. It's for a kitchen on the second floor. The height wasn't a problem for me, just the steepness!


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## demandrew (Dec 9, 2011)

COLDIRON said:


> Looking Good just like a Pro did it.


Thanks. Maybe that's what I'll tell people and see if I can fool them. How much do you think a pro would charge for a job like this? It took me a long time to complete but I imagine they could bop it out in half a day or so.


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## SPS-1 (Oct 21, 2008)

As Danny said in one of the first responses, check the installation instructions on the microwave. Do you NEED any venting at all? 
If the vent you have planned is rated at 300 cfm and says you need a 3-1/4 x 10 duct, and you put it through a 4" dia duct, well then, you won't get 300 cfm of airflow. Hardly the end of the world, unless there is some requirement for airflow to keep temperatures down.


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## demandrew (Dec 9, 2011)

SPS-1 said:


> As Danny said in one of the first responses, check the installation instructions on the microwave. Do you NEED any venting at all?
> If the vent you have planned is rated at 300 cfm and says you need a 3-1/4 x 10 duct, and you put it through a 4" dia duct, well then, you won't get 300 cfm of airflow. Hardly the end of the world, unless there is some requirement for airflow to keep temperatures down.


Thanks for the help. At this point the work has been done so there's no turning back really. I haven't actually bought the microwave either, but now I have the comfort of knowing that I can get that 300cfm without having to worry!


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## COLDIRON (Mar 15, 2009)

Thought I was done commenting on this however I just realized something.
You didn't even have the microwave or the installation instructions before you started this task.
I think maybe some of the responses would have been different.

The cart was before the horse, here's a potential problem you may encounter when installing the microwave.

Exhaust from microwave not lining up with hole in the wall and duct connection.
You should have had the microwave and the "Template" to get the exact location of the exhaust before starting the hole.

Oh well just an afterthought hope everything lines up properly for you.


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