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cluelessincolorado

Sigh - help make a hood decision :-)

cluelessincolorado
12 years ago

I have a GE Cafe AG range. The max BTUs are 20k,17k, 9.1k, 8k, and 5k. That's 59.1 k meaning I'd need 600 cfm if I had them all cranking at the same time. I won't. We do however quite a bit of cooking with the wok and frying. Now my question. Someone has offered a new Best hood with 1000 cfm for a crazy price and I am sorely tempted because I love the looks, the depth, and the material. Tell the truth, is it stupid to install this hood? The hood is 36" and the range is 30". I have a call into the city to ask about makeup air requirements. If they have them for this hood it's not happening. Thanks so much in advance!

Comments (8)

  • laranbrian
    12 years ago

    Sounds perfect to me! We put in a 1200cfm blower on a 48" hood over a 48" range. Any less size or power wouldn't cut it. Based on my experience the 1000cfm blower with a 36" hood over a 30" range should be nice.

  • cluelessincolorado
    Original Author
    12 years ago

    Thanks laranbrian! Just got off the phone with city. No actual cfm # that requires MUA, but you aren't allowed to have a pressure change of 3 pascals. Not sure how to determine THAT until hood is installed. We have a 100 year old porous house, but I sure don't want to be pulling air back through the furnace or water heater...
    "Ducted exhaust systems shall not induce or create a negative pressure sufficient to cause backdrafting of naturally vented, open combustion-chamber, fuel-burning appliances, or create negative pressure in excess of negative 3 Pa."

  • davidro1
    12 years ago

    House porosity is not a good thing because of the construction dust inside the wall cavities. You are better off opening a window even if the weather is too hot or too cold. Choose your air. Know where your air has been.

    Oversizing a blower is not a problem. You'll use the lower speeds more often. (Oversizing some other things does cause problems. (E.g. Air conditioning, if oversized, in a humid climate, gives you little to no dehumidifying so you feel clammy instead of comfortable.).).

    In Europe people eat good food too. They make do with less than 450 CFM in many expensive houses (that have room for wider ducting too). But, don't do anything just because wealthy people on another continent do it that way. Buy the bigger blower and enjoy it when you need it. I read here about someone who fried salmon in olive oil. I don't do that because salmon is greasy enough as is. Whatever floats your boat.

    To make the noise be mostly just wind moving and not any specific kind of motor hum or vibration, consider getting the blower installed in-line or outside ("external"). Moving the motor farther away gives you more room for other things up close. Either open space or more space in the upper cabinets.

    Finally, one thing that doesn't seem easy to get these days: a funnel shape of canopy so that the hood actually catches fast rising steam and grease, which comes in bursts sometimes. The filters are often built to be way too low down in the conical hood shape they sell you. There is a huge difference between a flat bottomed hood and another one that has a rim creating a few inches of space that catch smoke, greasy air and steam before the fan can suck it all away. (This problem disappears when you have a highest CFM blower and if it's already blowing at top speed when the burst of smoke happens.)

  • flwrs_n_co
    12 years ago

    It sounds like a great deal, but I think I would call the city back and ask them how the 3 pascals are measured and what happens if you exceed that measurement (is an open window sufficient?). I've been known to open the window a few inches even during a snow storm when I'm cooking and a hot flash hits, lol! I hope this works out for you since it sounds like a wonderful opportunity.

    In Jefferson County, I've been told we can only go up to 600 cfm without a make-up air system.

  • friedajune
    12 years ago

    I'd guess that the 1000 cfm hood needs an 8" or 10" diameter exhaust duct. What diameter is yours? Or, if you are installing the ductwork, make sure it is the diameter specified for that duct. If the duct is smaller, you will get more noise, and less efficiency through no fault of the hood. On the other hand, you say you don't even need 600 cfms. In that case, if your duct is smaller than specified, you likely can run the 1000 cfm hood on its lowest setting, to offset the noise.

  • davidro1
    12 years ago

    In general. you must have a duct of the exact size needed (specified by the opening at the exit end of the blower).

    If your duct is smaller than specified, you *could* run a large-cfm exhaust blower on its lowest setting (and think that this will offset the noise), but you would be UNsatisfied with the entire setup and UNhappy about the advice you thought you were getting from nice people advising what you can do.

    If the duct is too small from end to end it will resist or push back against air instead of allowing it to flow well; the fan blower will act in weird ways, humming, buzzing, strumming, and being generally lazy whether on speed #1, 2, or 3.

    Some ducts are only a few inches end to end. Some ducts are measured in inches length, because the end point is the wall outside, behind the hood.

    Some ducts go for so many feet that they need boosters (secondary blowers) at the far end.

    A long duct is an "obstacle", a clear resistance, a big thing. Never ask "is this considered long?" as it's all a continuum, from ease to resistance.

    If in the duct run, the duct diameter gets shrunk at a spot (a pinch point), this is not a serious obstacle. (web search "Venturi Effect" to read about air flowing around a point obstacle). Not a problem for air flowing through, but nobody will guarantee that the audible noise in the kitchen will remain low noise or pleasant.

    A duct could be made one size larger than the specified size. But not several sizes larger. If the duct is massively overdimensioned it can become too greasy inside (because in a duct that has fast-moving air, airborne specks of grease go straight outside). Microscopic grease particles, that filters won't catch, is what you perceive as "the smell of cooking". This smell *can* be eliminated but this costs so much that only a big restaurant might want to buy it.

    Your mission should you choose to accept it is to right size your duct, your blower, and your cooktop.

    Here is a link that might be useful: So how many CFM's do I really need (appliance forum)

  • cluelessincolorado
    Original Author
    12 years ago

    Thanks for the input everyone! I think my hesitation probably was my best indication about what way to go... Thanks for the link Davidro, this site is interesting in that just when you think you've exhausted all pertinent threads, a new one ( and the one you really need) pops up. Flwrs, if Jefferson is 600 cfm, it wouldn't be a stretch for Larimer to be close. The city left it up to the installers - HUH???

  • breezygirl
    12 years ago

    As long as your ducting is the correct diameter or you install new, I would definitely go for it. If you don't need that power, you'll run it at a lower speed most of the time. That's more quiet than running it on high! Quiet=good in my book. And 36" over 30" is a great size.

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