Recirculating Venting vs. External Venting in a Microwave Oven

12 Replies

Hi folks,

I just wanted to pick the brain of HVAC professionals out there regarding microwave vents for my rehab projects in Philadelphia, PA.

I have one of my GC saying we need to install microwave (with auto fan) vent that run from the appliance to outside. The vent affects the size of top cabinets I might be able to use.

Second GC is saying we do not need vent since microwave has auto fan.

Any thoughts?

Rehabbers out there..feel free to share your experiences and preferences.

Thanks a lot.


I have a recirculating microwave in my primary residence due to the location of the microwave. It's a little louder that and outside vented unit but I've had it for years and it's never been a problem.

Andresa Lobrace Would you install a recirculating fan in your bathroom? I doubt it! Why not? Because you want to remove the contaminated air from the house. The same goes for venting a microwave. Recirculation does absolutely nothing to remove odors, smoke or steam. The proper way to do it is to vent outside.

If someone cooks a lot of meat (grease) or uses a lot of heavy spices they would be better off with venting to the outside. 

Check local building codes, if its code then have it vent outside

If not needed by code I personally would still vent it out, its the right way to build for a number of reasons. Also, regarding cabinet heights, I usually have it go straight out the roof or at least into the attic then out a side wall of the house. This way it does not impact cabinets at all. Is that an option?

@Andresa Lobrace - there's no city of phila code (that I'm aware of at least) that requires exterior venting of a microwave. 

The last 3 apts I had.. all had tall ceilings and it would have been difficult (if not extremely ugly) to run the venting outside, thus we ran the recirculating.  I will say though that if your apt has 8' ceilings (or feels tight in the kitchen), I would try if possible to vent outside. 

Exterior venting as others noted, is ideal and preferred. If you're trying to have extra cabinet space, etc.. then you can re-circulate inside however as noted above, it wont remove odors, etc (vs. exterior venting). 

hope this helps

@Eddie Silva @Jamal Pitts @Jason D. @Manolo D.  @Max T.    

@Tom W.  

@Christian Wathne @Mike B.

Thank you all for the feedback. It has been very helpful.

Regarding Philly code, there is no specifications that I am aware of. The challenge here, specially in South Philly, is the low ceiling height and also the type of houses we have. Its one literally next to each other, making it only possible to vent to the back.

I always prefer to vent out on my rehabs and new construction. 

Again, thanks a lot.


@Andresa Lobrace I'm sure you know it's a expense price vs feature thing. If you're wall is already open, go, if not, then no. Personally I don't like fans who are recirc, it just filters the air instead of actually pushing it out, not all can be filtered btw, so you're breathing unclean air, but in most low end markets, it is not worth to spend the money when buyers/renters simply don't care.

Another thing to consider is that recirc fans do not filter air and as a result you may get a greasy film on the top of your cabinets over time.  Whenever possible add in a duct, will save you time in the long run (no more scrubbing greasy cabinets).