Hood size vs. CFMs

13 years ago

This is my first post here, though I've been lurking for a while and appreciate all I've learned already.

We are getting ready to start a kitchen remodel and have decided on a 36" range, either a BlueStar or an AG Wolf.

I know the recommendation is for a 42" hood for the 36" range, but we are tight for space, and I would really like to put in a 36" hood. Can we get away with the 36"? We don't fry or use a wok much at all, though we do use quite a bit of garlic, and maybe once a month or so cook something like bacon.

My first choice would be a 36" Vent-A-Hood with a 600 cfm blower, but the salesperson recommended a 1000 cfm Kobe. What would you choose?

Thanks for the input.

Comments (11)

Fori
13 years ago
I would choose the 36" VAH with 600 CFM. I'd only bother going wider if you were a mad stir fryer OR you had an island or otherwise open area.

(I have a 36" 600 CFM over my 36" cooktop and don't need more. I can kill the bacon smell. If I want to, that is.)
juniork
13 years ago
Definitely don't get the 100cfm kobe. We have a thermador 36" in our current house, with a Kobe (I'm assuming it's low cfm), and not only does stuff still get greasy (like the cabinets above the hood, the hood itself), but because it's 36", the upper cabs on either side of the hood also have gotten a nice build-up of grease over the years. sigh. Did I mention we have cleaners every 2 weeks?

Next house, I'm getting a 36" blue star or capital, and SS backsplash, and the strongest 42" hood I can afford!
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For the benefit of anyone else checking out this older thread, let me clarify that cfm only tells you the power of the blower with nothing attached, not the actual draw with a real hood and ducts connected to it. The size of the ducting matters a lot and if your model only has 6" ducts you won't get above 600cfm of real draw regardless of what the blower can do sitting by itself. If you care about a powerful draw to capture the heat when there are lots of burners going or the oil vapor, odors etc., go for a hood with 8" ducts (the spec sheet on line will tell you their diameter) and intake filters that extend over as much of the underside of the hood as possible. Weird shapes that look as if they let the fumes escape... probably do let the fumes escape! That said, if you are not cooking on 6 burners at once or something truly smelly or oily, you may never want to turn the blower on full blast. No point buying a car that can hit 120 mph if the speed limit is 65 and the traffic is always slow. You may be paying a lot for a blower with power you'll never use.
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In the interest of brevity, (for prolixity search this forum on keywords such as plume, effluent, MUA, hood, etc.), here are a few maxims: The air velocity at the baffles has to be high enough to keep the rising and expanding cooking plume from reflecting down and out of the hood. This value is proportional to the velocity of the rising plume, which is proportional to the temperature of the cooking surface (for large surfaces), and of the flame combustion product (for small surfaces, large flames, and obviously gas cooktops). I recommend 90 ft/min for general all-purpose success, but with modest induction cooking, you might get away with only 60 or 70 ft/min. Feet per minute is equivalent to CFM per square foot of hood entrance aperture. The hood entrance aperture should overlap the pan surfaces by enough to encompass at least a 10-degree half angle from the contour of possible surfaces bounds (except where constrained by a wall). Obviously, as the hood height is increased, the size has to increase to meet this angle. From the above two results, the required total flow rate (CFM) is calculated. Duct diameter should be such that the velocity of the air inside is in the 1000 to 2000 ft/min range to minimize grease deposition. The higher end of this range may be best in warm climates. Blowers are usually rated for flow rate at zero static pressure, i.e., hanging in the air. In a ventilation system there is restriction that causes pressure drops (called loss). As pressure loss increases, flow rate decreases according to the fan curve of the blower. The CFM rating should be some multiple of the CFM required. The exact multiple depends on many things, including the fan curve, different for each blower, and MUA restriction. I recommend using a factor of 1.5 to be safe with open windows for MUA. (Note that screens will have a pressure loss depending on the open window space.) I will skip MUA maxims in this message, as open windows in southern CA should be adequate. Please search on MUA to find out about hazards of low interior house pressure with combustion appliances. kas
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trailgirl
13 years ago
Well, we are getting a 36" Blue Star range with a 36" Kobe with 1000 cfm. It's not installed yet, so I can't tell you how effective the set up is. Our good friends have a 48" Blue Star with a 48" Kobe and love it. All the appliance people we spoke with said 1000 cfm would be fine, we were more than willing to listen to any arguments for a larger set up and no one tried to sell us anything bigger. Anyway, I think my DH liked the nifty lighted controls on the Kobe.
breezygirl
13 years ago
Juniork--OP said 1000cfm, not 100.

I'm trying to find the right hood for a Capital Culinarian 36" rangetop. I have thought about a VAH, but have second thoughts with many bad reports of their noisiness and difficulty of cleaning. Some of the noise issues may be because of ducting issues, but I'm not sure I want to take that chance. Kobe has a solid reputation over on the Appliance Forum. Have you done any research over there? Warning, you may become even more confused if you read too much about venting like noise, internal blowers, online blowers, make-up air, etc. Speaking of make-up air, have you checked your local codes to see if you'll need it? My local code requires it for any hood with 400 cfms or more.

I would recommend the Kobe for the baffle filter, quietness, and higher cfms. With higher cfms, you won't have to turn the hood on as high to get the venting you need most of the time. Lower speed equals less noise.
montel (CA US 10b/Sunset 16)
13 years ago
Also, another thing to consider is when you go with something as powerful as 1000 cfm you will need some sort of make up air - or you risk pulling air, ashes, combustion gasses from fireplaces, furnaces etc...

In our new home, which is well sealed, with "just" a 500 cfm fan we are going to install a MUA damper and air vent to bring in fresh air. This is now code for most locations.
deeageaux
13 years ago
VAH is a SOB to clean.

I would absolutely get the Kobe.

Kobe can be difficult to install but once you are done with that you are done Kobe's pecularities.

VAH's cleaning issues are ongoing.
eandhl
13 years ago
The Kobe will be much quieter.
momtotwinboys
Original Author
13 years ago
Thank you very much for your advice. I was worried about the Kobe because I have read so much more about the Ventahood, but am now feeling much better about it.

I don't think we have to worry about the ventilation in our house and the 1000 CFMs because our house was built in 1928 and is far from airtight.
breezygirl
13 years ago
You do need to check into your code requirements for MUA even if you have an older house. In my area, MUA is code regardless of house draftiness.

Justbecause you've heard about VAH more often, doesn't make it better. :)
juniork
13 years ago
oops, breezy, you're absolutely right! I change my opinion! I would go with the 1000 kobe, as well. Are they about the same price? I found a 42" kobe for about $1500, but it looked as though the same size vent-a-hood would be more like $2000
weedmeister
13 years ago
Will you have cabinets on either side? if so, then the 36" should work just fine. With nothing on either side, larger is better. The 'fumes' spread left/right/forward so capture area becomes important.

Hood size vs. CFMs

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Fori

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Hood size vs. CFMs

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