can I add a blower to my externally vented microwave to increase cfm?

3 years ago

I have a GE profile over the range microwave that is vented through the cabinet above it to outside. I was thinking of getting a professional oven and wanted to increase the CFM of my microwave system. I would turn off the internal blower on the microwave and install the more powerful blower in the cabinet along the vent. Is this possible? Could I get 600-1000cfm or do I need to just suck it up and pull out the microwave

Sort by:Oldest

Comment (1)

kaseki
3 years ago
Indeed, the microwave oven has too little spare room to have a decent duct. It doesn't even have a decent filtering scheme.

I will note that in a previous lifetime, I had a TRW cooking center that had cooktop, oven, and microwave. The ventilation was minimal from a small fan blowing into a 4-inch duct. I added a modest NuTone downblast blower to the roof and upgraded the duct diameter between roof and cooking center. This ONLY helped because the cooking center had a pop-open "eye-brow" vent above the microwave oven that had a decent aperture (for its time). So the combined cooking center exhaust flow via its 4-inch duct was merged into a 6-inch duct and thence made its way to the roof blower. This did aid kitchen ventilation some, and even the flow into the microwave oven part of the path. But by today's standards, and perhaps even yesterday's standards, the overall capability was wholly inadequate.

Presently, that roof blower is connected via a 8-inch duct and silencer to a pair of ceiling registers (with furnace filters) for the purpose of collecting, as best it can, oven effluent. I haven't been able to find the rated blower CFM, so I can't supply that at present for comparison.

The basic issue with boosting a microwave oven air flow is, as @User noted, the gagged air path in the microwave oven structure. Typical blowers one might consider for boosting this can not pull more than a few inches of water against the microwave duct, so the actual flow will likely go from 50 CFM to 100 CFM at considerable effort to miminally improve the air flow. Blowers that could boost the flow significantly are far too loud for consideration.

A "professional oven" with assumed "professional cooktop" will need a larger hood just for capture of rising and expanding cooking plumes. For containment, the flow rate into the hood aperture should be roughly 90 CFM per square foot of hood aperture. So "professional" cooking equipment will require "professional" grade ventilation. And MUA will be essential.
Related Discussions
Venting: highest CFM for 9' duct, internal blower)
Q
Comments (7)
Stephanie: 12'' duct is very unusual in residential units. All units I've seen have spec'd 10'' duct as a rule. One option to discuss with your HVAC contractor would be to use rectangular duct for the constricted area. It's a bit more constrictive than round duct, but, for example, a 18'' x 4'' rectangular duct will squeeze through small spaces, and then you can run 10'' duct on either side of that. While it will act as a bottleneck, its effects should be modest, and certainly superior to using 8'' or 9'' duct throughout. In either case, you are best off with a better quality internal blower. The one that MA uses is designed to compensate for back pressure of long duct runs and will maintain flow rates even through rather high resistance. May be a bit noisier than 10'' duct but remember that with the MA you'll have an infinitely variable speed control and you'll find that you run at far below full speed most of the time anyway. I have little doubt the MA with 1200 cfm internal blower will outperform the VAH--particularly if they are quoting their mysterious "equivalent cfm" which means the actual cfm rating would be only 800 cfm to start. PS: sfjeff: two single quotes ' ' typed in succcession will be "seen" by GW as double quotes, for the "inch" sign.
...See More
Help I Need a High CFM Gas Dryer That Can Tolerate a Long Vent
Q
Comments (12)
If you're sure that your vent line has no built-up lint or other obstructions for its entire length, then a dryer vent booster fan would almost certainly solve your problem. The booster fans from Fantech are completely automatic. they switch on when air pressure builds up in the vent line from the dryer fan running, and turn off when the air pressure subsides. They have both in-line models and models that would mount on the wall at the end of the vent run. More info available at the linked website below. Here is a link that might be useful: Fantech Dryer Booster Fans
...See More
Can I use microwave ducted vent for recirculation exhaust venting?
Q
Comments (14)
I think the key word above is "appear" because to me these OTR microwave ovens look like they are not flush by two or three inches. From an earlier post: "If I can use the top vent [to] go up through the cabinet and resolve the ductwork above that cabinet, that vent will care for the stove venting and the magnatron venting, and I would not need a MW with a front-facing louver." In my view, neither this nor any other microwave oven venting scheme I'm even vaguely aware of will "care for the stove venting" because they move far too little air per unit time and the units do not overhang the burners sufficiently. Perhaps if a supplementary blower designed for higher pressure loss is used in the path taken by the this so-called ventilation to augment the flow rate, barely adequate air flow will be possible. But even then, capture area will be too small to have much effect on front burner plume capture. You can design for style and give up on having adequate ventilation, or design for adequate ventilation and give up on OTR microwave ovens. Your statement "For what it's worth, most of the cooking on our stove is boiling water or soup, scrambling eggs, or simmering an occasional kettle of sauce." suggests that you can get away with doing the former. In that case, provide manufacturer specified cooling paths for the magnetron, and ignore limitations of the mediocre or worse ventilation. And don't sear steaks on the cooktop before baking them in the oven.
...See More
External blower CFM question for old house kitchen, 40' vert roof duct
Q
Comments (20)
The way I think about it, a 7x7" duct is 49"^2, whereas a 8" circular duct, which seems standard, is around 50"^2, so it's quite similar. The actual math is a lot more complicated than that. It generally requires solving partial differential equations which is not something I am prepared to spend my time on. But assuming you actually have a full 7x7" and smooth wall surfaces, there is an approximation that should allow you to estimate the equivalent dimension of a round duct: Deq = 1.3*(x*y)^0.625 / (x+y)^0.25 = 1.3*49^0.625 / 14^0.25 = 7.652 If we assume laminar flow (probably not quite true, but a fair approximation as long as the walls are smooth), then the Poiseuille equation applies. It states that the flow rate goes down with the fourth power of the radius. For a 7x7" duct, that would be about 16% less than a round 8" duct or about 65% less than a round 10" duct. Additionally, the flow rate goes down linear with the length of the duct. Let's say your 40' duct is about 5 times longer than typical residential ducts. Let's also assume that hood manufacturers would normally recommend a 10" round duct for the type of hood that you have. Then you only have about 7% of the capacity that the manufacturer recommends. The biggest problem is obviously the length of the run. But the dimensions are also a very real factor. And the smoothness of the walls (if the duct isn't lined with metal but maybe just brick) shouldn't be neglected either. In an ideal scenario, you'd either find a different location for where to vent to the outside resulting in a significantly shorter duct, or if that isn't an option, you'd increase the diameter of the duct dramatically. Something like 12x12" wouldn't be a bad idea. It's probably OK if you have to reduce back to 7x7" for the last two feet on the roof.
...See More

can I add a blower to my externally vented microwave to increase cfm?

Comment (1)

kaseki

Related Discussions

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US