Seeking advice: microwave range hood doesn’t exhaust well

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This topic contains 12 replies, has 10 voices, and was last updated by  chkelly80 2 years, 11 months ago.

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  • #1305

    Jon
    Member

    We moved into a house with a fancy GE microwave above the glass cooktop. It exhausts to the outside. The damper on the wall cap blows open when the vent fan is turned on, and you can feel air movement. However, steam from boiling waiter doesn’t seem to get sucked into the hood very well. I’ve checked the metal mesh filters. They looked clean but I rinsed them anyway. The ducting between the microwave and the wall cap is all enclosed – short vertical chase and then it runs horizontally between the ceiling joists for about 8 feet.

    Any tips on improving exhaust performance? It’s not enough of a problem to get me to lower the microwave and remove the wall cap to check/replace ducting. Thanks in advance.

    Jon

     

    #3388

    The Advisor
    Keymaster

    Microwave range hoods are more microwave than hood. Their ventilation performance is an after thought. Bad ventilation is designed into the them.
    Taking that as the starting point, you may have other issues too. The duct run seems short enough, with either 1 or 3 elbows (depending on how the duct gets out of the house through or under the joists).

    Microwave vents usually have an option to duct back into the kitchen, I just don’t recall if you can redirect the air flow after installation. If you can change the air direction into the kitchen, I would do that to see if the venting improves, thereby learning if there might be a problem in the duct work. Do you have a wire mesh at the exit blocking birds and nest building?

    #3393

    Bermuda Bob
    Participant

    Jon, there are two (2) aspects I’d be interesting in knowing …

    1. What is the CFM rating of the blower ???

    2. What is the "run" of the duct vent to the outside ???

    One more pont you need to remember … steam begins to cool quickly as soon as something (like you hood) begins to move it away from the heat source which created the steam in the first place, so the further the actual hood is from the cooktop is a major consideration … another might be if A/C is close enough to the cooktop to affect things !!!

    #3394

    Cohiba
    Participant

    Jon … when GE invented the SpaceSaver Microwave (now generally called an OTR) back in the mid eighties, they probably figured that most consumers just use their hood as a lampshade for the cooktop light anyway and rarely turn on the blower. Their units were something less than 300 CFM (270 if memory serves me) and at the power level under perfect conditions it would take a little under three minutes to ventilate a 10×10 kitchen. Of course conditions are never perfect. Try turning on your hood before you need it … before you start cooking. Turning it on early will create a draft that might help solve your problem

    #3395

    Appliance Stallion
    Participant
    See if someone can install a remote blower in your attic or on the roof. That will suck the life out of your cooktop steam.
    #3396

    Bermuda Bob
    Participant

    … the cooking area of the kitchen will be a "No Toupee" zone !!! HeeHeeHee !!!

    #3397

    tagoneo
    Participant

    Jon, you suffer the dilemma of many homeowners. Over the range microwaves have become very popular, driven by what people want, not necessarily by what they need. If you are not cooking on the cooksurface much, then an OTR is fine and convenient. However, anyone who cooks a lot will hae an OTR once, and then will do what I am suggesting to you, which is to replace that OTR with a range hood of sufficient power.

    All OTR’s are either 220 cfm or 300 cfm. 300 cfm is what a high quality bathroom fan vents at. It is barely adequate for a range. The simple math for doing ventilation is this: If you are using electric, 300-400 cfm on a hood (not OTR) is sufficient. For gas, the math is this: Add up the BTU output of the surface burners, and then divide by 100. This is the amount of CFM’s you should have in a hood, given a proper installation. This of course is assuming that you are venting to the outside and have proper exhaust duct size.

    Your other problem is that an OTR is nowhere near proper sized for anyone’s range – the scoop, or intake area, of an OTR is not deep enough. If your range is 26" deep, but your OTR covers only the back 15", you have no capture area above the front burners. This is why range hoods stick out so far. If you want it to work right, it has to cover the cooksurface.

    My recommendation: Turn the OTR on a minute or twobefore you start cooking, to start a flow of air in the direction you want. This will create an airflow pattern pulling into the OTR. Try to do more cooking on the back burners.

    Otherwise, you could go with a remote blower as someone suggested, and you can mount it on the side of the house, as long as you don’t mind seeing a 20" x 24" x 10" box on the side of the house. Don’t go over 600 CFM, as your 3 1/4 x 10 or 6" round ductwork will restrict are movement greater than that, plus if you do go remote blower, you will want to take the OTR down, remove its internal squirrel cage blowers (very simple to do) and reinstall the OTR, so as to not have an obstruction to airflow. Be ready for some whistling noise when you run that remote blower on high though. You will also need a wall switch to run the remote blower. They are available, talk with a local REPUTABLE appliance dealer. Big bog stores will look at you and say "huh?"

    If you do what I just suggested, one thing to keep in mind – most OTR’s nowadays use the exhaust fan to cool the internal workings of the microwave when cooking. If you remove the OTR’s blower motor, and your OTR does in fact turn on its exhaust fan for internal cooling, you will need to run your remote blower every time you cook, or you will burn up the mag tube or high-volt transformer in the microwave.

    I would suggest you just deal with the OTR for now, or take it down and replace it with a 400-600 CFM range hood and put a cheap disposable microwave on the countertop somewhere.

    #3398

    Ed Smith

    Kitchen Appliance Sales/Customer Service Professional

    Allentown PA

    Jon,

    Unless you’re planning a kitchen remodel this is probably something you’re just going to have to live with

    As other posters said the Microwave hood is more microwave than hood and has a low CFM blower. You don’t mention whether you’re cooking with gas or electric. Unless you’re planning to do serious high heat wokking or grilling on a high output burner you will probalby be ok and just have to rush to open windows if you burn bacon or somthing.

    #3400

    Jon
    Member

    I think I’ll just turn the vent fan on early and live w/ existing situation. In answer to some questions, wall cap isn’t screened, glass cooktop is electric, vent only has one elbow. I’m definitely not going w/ a countertop microwave and true range hood because this galley-sized kitchen has precious little counter space to begin with.

    Not only that, but the natural draft water heater already fails a worst-case depressurization test, (but drafts fine under actual conditions), so a proper range hood would need a make-up air supply.

    Jon

    #3401

    Bermuda Bob
    Participant

    Jon, one more thing … I sometimes part company with my brethren in the Appliance Industry, but I am not a big fan of the "over-the-range" microwave – aka OTR – because all of us can recall grabbing a vessel in the microwave and quickly discovering it was too hot to handle !!! Now, if you were to pull that vessel out and drop it because it was too hot to handle, you’d be dropping onto the RangeTop or into, possibly, a pot of water, sauce, etc. …

    Get the picture ??? You have indicated that you have an electric glass-top range, so that’s a plus, there are many horror stories about people with loose clothing reaching over a gas top, being set afire, and suffering severe burns … and, in one case I know of, death !!!

    I have always had my clients who insisted on an OTR to provide me with a letter which sez that I explained the negatives about an OYR, so I implore you NOT put the MicroWave over the CookTop !!!

    Countertop space is easier to create than new skin, or a life !!!

    #3984

    adam007
    Member

    Check the duct that is it leaking from some place between your microwave and wall cap? Definitely your duct’s cap is close but it can be leaked from somewhere.

    #4560

    Bucky
    Member

    I have been in plenty of conversations of a similar capacity and the consensus seems to be that everything is going to be okay in your situation. If anything I would call an independent repair guy like myself to come over and break into the hood and see if he can’t get things flowing the way they are supposed to. The only main issue I have ever really seen in a case like this is vapor accumulation on a painted wall in the kitchen and that was in a very poorly made apartment.

    #7670

    chkelly80
    Participant

    I have the same problem: even though my microwave is vented to outside, it just does not do an adequate job. I am almost ready to ditch the microwave and put a range hood. Before doing that, I would like to know if putting a inline duct fan on the microwave vent is a possible solution. Someone suggested it but I am not sure if that is doable or if that will solve the problem.

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