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flush mounted ceiling hood

Posted by carnegiedunn (My Page) on
Tue, Jul 17, 12 at 17:21

I found a ceiling-mount range hood that I think would look great in my kitchen, but I have a couple of questions...

Duct:

Since this hood has 2 separate blowers, any advice on how the duct should be set up? (visit link to see picture drawing)

Height:

I can have it flush mounted into the ceiling - 9 feet 6 inches, or have my contractor make a soffit box, let's say 9 inches deep, so the hood would end up about 8 feet 9 inches from the floor. Do you think the difference in height will make a difference in suction? Considering it has 2 blowers...

P.S. If anybody has actual experience with a kitchen hood that's in the ceiling, I'd love to hear your thoughts. It seems cool, but it's just so different I don't even know where to start looking for potential pitfalls.

Here is a link that might be useful: Skylight ceiling hood


Follow-Up Postings:

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RE: flush mounted ceiling hood

A hood aperture at the ceiling needs to be fairly large, ideally at seven feet extending about 20 inches beyond the locus of points that consititude the edges of pans on burners projected vertically to the ceiling. At 9 feet the overlap should be 25 inches larger. (These values are based on a 22.5-degree effluent expansion angle, but rising effluent angles have been measured at lower heights, so cooling effects might make the rising effluent shape less conical up high and allow some reduction in size.)

Flow rate (cfm) has to be larger proportionately to the larger aperature area of the high hood. Proportionately larger make-up air supply will be needed in many cases.

Design should approximate commercial hoods (without the fire extinguisher) which are typically mounted that high.

In any case, the higher the hood the more easily effluent can miss being captured and contained due to air turbulence from drafts, people moving, etc.

kas


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RE: flush mounted ceiling hood

Thank you for such a detailed (and a little overwhelming!) explanation.

This hood is 54" wide x 25" deep, and it's going over a 36" cooktop.

If the cooktop is 36" x 20", then there's 18" extra width and 5" extra depth on the hood - a little less than your calculations... but it's not like I'll be using all the burners all the time - maybe 2 or 3 max. For airflow, it's got 2 blowers with 940 cfm each. So, except for Christmas and Thanksgiving dinners, I feel that it should be adequate... what's your call?

Also, regarding mounting height - if I tell the contractor to make a soffit box maybe 8-9 down from the ceiling, will that make a major difference? I'd rather have it flush to the ceiling, but I can tolerate a soffit, IF there's a good reason for it.


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RE: flush mounted ceiling hood

I'm going to try to translate for kas, who, surprisingly, is being rather polite in his recommendations. I'm not so kind. I find this kind of concept is ridiculous, unless you have no interest in actually doing any useful ventilation. It's all for "show", not at all for "go."

I don't think you get the implications of kas's calculations. At nine feet ceiling height, the outer edges of the hood need to be 25'' bigger on all sides! That means, given a 36'' x 20'' cooktop that it would need to be roughly 86'' x 70''--that's right, 7 by 6 feet, to have adequate capture. Your proposed 4 x 2 foot unit would be an epic fail. As kas said, for this to work it would need to look like one of the huge hoods you see in a commercial kitchen. Nothing at all like the cute picture on the Futuro website. That's just useless.

Dropping the ceiling down with a soffit by 9 inches (assuming that's what you meant) reduces the dimensions needed by something around 4'' on each side--a meaningless difference.

You can install a hood for ventilation, or for style. If all you want is the latter, go for it. But don't expect any useful ventilation.


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RE: flush mounted ceiling hood

Well, since you've brought up "ridiculous", I think that the concept of 7 x 6 foot hood is ridiculous. I'm not running a pizza oven, it's just a little 5-burner cooktop. I don't think a 7x6 foot hood even exists! How would you ship something like that? Or get it into the house?

If I wanted to hang a huge monstrosity in the middle of the kitchen, I'd go with a Ventahood and be done with it. But I don't. I want it to be as invisible as possible, which this skylight hood does perfectly. Besides, I don't think 2x 940 = 1880 cfm is "all show, no go". There HAS to be an effect from this much airflow. I would understand why you would need a make-up air system for this kind of power.

I get the objection about "higher height = bigger hood", but at some point, wouldn't you throw the standard templates out and just consider the effect on the whole room? This is why I was asking for feedback if anyone has a similar type ventilation system, based on just sheer airflow and not pedantic adherence to formulas...


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RE: flush mounted ceiling hood

Sure, I understand your concerns, and if you can find someone who has a similar hood setup and finds that it works great, more power to you.

I agree totally with you that a 7x6' hood is ridiculous. That's really the point--that fundamentally, the concept of an "invisible" hood in the ceiling just doesn't work. It's simple physics, as kas was trying to point out. As the plume of effluent rises from your range, it inevitably spreads out laterally in all directions, in a pattern than can be roughly approximated as a cone with sides angled at 22.5 degrees. If your hood is not large enough to capture the effluent as it spreads laterally, it cannot contain it and then evacuate it through your ductwork. No amount of airflow, no matter how great, can compensate for lack of containment, short of flow that is so great that there is a true vacuuming effect. That is not achievable with conventional blowers--certainly not 1800 cfm. If you're talking about 10,000 cfm, maybe you start having a point. But then we're not talking hood vents, we're talking HVAC at that point.

I still disagree that all vents are ugly. For example, see the top right image here:

custom hoods from ModernAire

While this kind of unit is still substandard in performance, it's a heck of a lot better than trying to suck everything up at ceiling level!


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RE: flush mounted ceiling hood

It's beyond useless because it gives the illusion that the purchaser is actually managing to vent their kitchen properly. It's like trying to light your kitchen with a single 60 watt bulb from a 10' ceiling. It might be marginally better than nothing, but it's not ever going to be a substitute for the proper technology.

I suggest you visit some showrooms with island vent hoods installed. You will not find them all that obtrusive and you are sure to find something that works about 1000% better.


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RE: flush mounted ceiling hood

Those "hoods" are for people who only microwave leftovers. If you fit in that category, go for it. If you aren't, then you need to get serious about finding something that actually works first, and then secondarily satisfies an aesthetic.

Or move that cooktop to a wall where it's a heck of a lot easier (and cheaper) to vent it properly. You only spend 10% of your time in a kitchen applying fire to food. The vast majority of "cooking" involves prepping the food to be cooked. That takes up 70% of your time. Figure out a way to maximize the sociability of that task by maybe putting a prep sink on the island instead and relegating the fire to another location.


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RE: flush mounted ceiling hood

I'm definitely in hollysprings camp. I think islands are a poor place for a range. Conversely they are often great places to do prep, have seating areas for bar and food service, to place storage or appliances underneath, etc.


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RE: flush mounted ceiling hood

If you like aerosolized grease all over your ceiling and cabinets than go for this hood. I can't imagine this hood working any better than opening a window.
You need a real hood mounted 30-36" about the cooktop if you actually want it to work.

Also, unless you have a huge leaky house you WILL need makeup air with an 1880cfm vent hood code or not. Depending on where you live you will need to condition this make up air which will cost you at least 7,000-10,000.

I don't know how big your house is but lets assume it's 3,000 sq ft with 10 ft average ceiling height. You will evacuate all the air in your house every 16 minutes.
Good luck


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RE: flush mounted ceiling hood

Normally we speak of capture and containment as the primary duties (required capabilities) of a hood, and these usually require a modest sized hood 2.5 to 3 feet over the stove. There is a third capability of a hood, removal of air from the house. If the hood is too high for its size, then smoke, moisture, odor, and grease particles from cooking permeate the house, or at least the kitchen if the entry passages are small. Those portions that stay aerosolized will eventually be removed with all the air being moved. Some will condense on the walls, ceiling, floor, cabinets, curtains, etc. Thus, the hood will appear to remove it all, eventually, but surface cleaning will reveal why immediate removal is preferable.

kas

Clin: "surprisingly"? :)


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RE: flush mounted ceiling hood

Kas: I was struck by the remarkable restraint that you exhibited (and I lacked). Your post had the requisite information, but I could not resist pointing out the implications in a more direct way--a 7x6 foot hood!

To the OP: it is, unfortunately, an act of faith on the Appliance forum, that ventilation performance of a hood is ranked somewhere below godliness, but above most other attributes. This is due to a small, twisted, but very vocal group who truly obsess over capturing every molecule of effluent produced by their ranges. In that world, there is no question that a ceiling mount hood is blasphemy. And, we're right, such a hood will do a really lousy job of ventilating.

However, it should be pointed out that those outside the lunatic fringe may rightfully believe that aesthetics are as, or even more important than ventilation performance. A ceiling-mount hood is just fine as long as you have reasonable expectations--that it will wow the neighbors, but will also fail to prevent the smoke detectors from going off when you try to really sear a steak properly. That'a a tradeoff that may be just fine for you. Not for me, but possibly for you, as long as you know what you're getting. It's like those Gaggenau show kitchens--they are awesome as long as you don't actually cook in them. There are plenty of folks who would choose that over my now battle-scarred Lacanche range (with fabulous ModernAire hood). But I built my kitchen to cook first, impress neighbors second (though I still think it does the latter too!).


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