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Angled hood

Posted by Co.lin (My Page) on
Thu, Jan 26, 12 at 13:08

I'm considering a diagonal range hood, but I've seen some negative feedback on such hood shapes - but nothing really definite. It seems that it's less effective than a "flat" hood... is that true? How much less effective? I cook maybe 2-3 times a week, of course it gets crazy around the holidays, and I'm wondering if the difference in its effectiveness is major, or just a few percent? Does anybody have a diagonal /angled range hood, and if so, what's your impression?

Here is a link that might be useful: Angled hood of my choice


Follow-Up Postings:

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RE: Angled hood

It will be less effective than a correspondingly-sized "hood" unit. Without doubt, more of the cooking steam/smoke/grease vapor will escape than had you chosen a more utilitarian vent. But it'll get some of it.

I think my BIG objection would be the fact that the freakin' lights are shining in your face. THAT is annoying. Who needs lights shining in your eyes when you are cooking? Can you find something that has lights angled down toward the cooking surface, instead?


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RE: Angled hood

Commercial hoods are required to be steeply angled, aren't they? (I only know from watching TV, but I think one of the experts here also said it was better from a physics point of view.)

Totally agreed with Mojavean about the lights on that particular hood.


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RE: Angled hood

From the technical point of view, yes, diagonal hoods do tend to have worse performance than flat ones. That being said, I looked at the link you posted, and after reading the technical specs, I can say there are 2 things about this hood that offer a saving grace. One, the perimetric suction, which creates a "wall effect" instead of the more dispersed suction pattern of standard mesh filters, and two, it has a 940 CFM motor, which provides a relatively high amount of airflow. So if you do not cook a lot or get into heavy frying, and you're that much in love with the style, it should be adequate. I would still recommend a flat hood, but that's just my professional opinion. After all, it's your kitchen, not mine, and you'll be looking at it for the next ?? years.

About the lights... agree with mojavean and pillog on the subject of lights in your face being a major annoyance, but fluorescent lights are less harsh than halogens, and the lights on this hood design are pretty far apart.

And now, I have a question for you... is this hood going to be installed on an outside (bearing) wall, or an inner wall (between rooms)?


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RE: Angled hood

Commercial hoods have large overhanging sides to ensure capture, and sufficient vertical depth and high flow rate to ensure containment. The baffles are steeply angled (by code) to cause the grease to drain better to where it is collected, thereby reducing fire risk. The usual commercial configuration bears no resemblance to this Futuro Futuro.

Further, this Futuro "hood" is insufficiently deep from the wall for most cooktops and ranges, as it should extend to beyond the surface area of any pan being used on any burner. It may work ok for pans on back burners.

Hoods to not work by sucking air from the vicinity of the cooking zone. Expanding effluent that rises from pans beyond the overhang of this hood will escape into the kitchen and will be removed slowly as part of the household air that is finding its way to the hood over time. By then signficant grease may have been deposited on surfaces and odor will be everywhere.

If this unit actually pulls 960 cfm, you may need a make-up air system.

kas


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RE: Angled hood

kas is just being nice about what he thinks of this hood.

I don't think you could design a hood less likely to work well. The angled, flat plate design is way too small in capture area, and the angling would really encourage ineffective capture by routing effluent forwards rather than temporarily capturing it long enough for the airflow to remove it. Simplistically, think of taking a flat sheet of steel and trying to use it to repel the spray from a garden hose. Would you hold the plate perpendicular to the direction of spray, or would you angle the plate to the side? Obviously, the latter approach allows the spray to ricochet off and a significant portion will end up getting past the sheet.

I also agree with kas that the "perimeter suction filter system" seems unlikely to improving things much. At the flow rates achievable with this kind of setup, you cannot create a "wall of air" that somehow would trap effluent. Those effects extend only a few centimeters past the edge of the slot at best. And I'd also worry that trying to channel 960 cfm through a few thin slots is likely to reduce the functional flow rates way below that rating.

Futuro is a leader in hoods that sacrifice performance for style (not all of them, but many). That's fine--for many, the look of the hood is more important than whether it actually works. But I wouldn't make any false assumptions about what this hood will do, ventilation-wise. Heat a cast iron skillet for 5 minutes over 20K BTU burner, throw on a heavily marbled piece of beef, and expect to be running to shut off the smoke alarm in the next room.


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RE: Angled hood

One point Kas; were this hood installed in an In 'N Out Burger, then I would agree; significant grease would be deposited. This hood is going in a private home where the OP has stated they cook "2 or 3 times a week."

They will probably be okay with a hood that doesn't look like it escaped from a Denny's. Furthermore, we have had several GWers over the years who have installed similar angled hoods and loved them.

Stove, hood, and counter

Here's one from this thread from 2009.

While they do not present the optimal umbrella capture shape to get most of the plume, they also don't get in your face when you are cooking, hover over your head, interfere with your spatula-waving or pot-sniffing, and don't harsh your tall-pot mellow, either.

They can be, as seen in the photo above, incredibly beautiful.

There is still something to be said for beauty.

The optimal outfit would be sturdy shoes, comfy trousers, a loose shirt and a hoodie. Thank goodness this advice is

Photobucket
not always heeded.

I contend that esthetic considerations, personal preference and decor selection, and the overall workload of the kitchen in question could lead a person to select an angled range hood and be happy with the result.

You are completely right about the makeup air issue.


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RE: Angled hood

@mojavean: cute, and your points are well taken. However, I'd argue that the Futuro is NOT the LBD of the ventilation world. LBD is all about simplicity, fundamental design over embellishment, timelessness, in many ways, the fashion equivalent of "form following function."

So...to me, this is the LBD of ventilation hoods:

Photobucket

In contrast, I see the Futuro angled hood as an example where function has been totally sacrificed to form. So, the fashion equivalent is really more like this:

Photobucket

:-)


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RE: Angled hood

While I don't think you are completely wrong, clinresga, I think you are missing a facet of this hood that could, possibly, perform better than the way you visualize it. Let me get out my drawing tools here ...

Okay, first up, here is a picture of how I visualize a "flat" hood, something along the lines of the modernist glass plate designs you see coming out of Italy a lot.

Photobucket

For this thought experiment, lets think of all the burners on the range on and cooking at once, although this would usually be quite rare.

As you can see, our plume begins to expand the second it escapes the cooking surface. The heated molecules both rise and "plume" outward. Assuming a 1m/sec speed at escape from the pan, the plume is not under any influence from the hood itself it encounters the currents of airflow caused by the intake blower. Molecules from the plume will be diverted toward the intake aperature as they approach the hood itself, but if they impact the plate, they will have to turn 90� *toward* the intake aperature in order to be entrained in the exhaust flow. If they divert the other way, they will very likely escape.

To me, this alternative is probably the worst design.

Next, let's look at your hood, the best design. We will call it "The Holy Shroud"

Photobucket

Obviously, of all the alternatives, this it the best design in terms of ensnaring of cooking fumes. Very little can escape its mighty power of suckage! Do we really need to go over that again? NO! This is the best!

BUT ...

Now let us look at the poor, disrespected and abused "Angled Hood" For this exploration, let's step to the side of our imaginary range and hood like so:

Photobucket

Okay, first of all, even though the hood is angled, it is not "pushing" anything toward you. The plume will hit it and the upward force of the lighter gas will combine with the angle of the hood to "duct" the flow upward along its surface. A 45-degree turn. That flow will then encounter a rather strong intake flow the second it crosses an intake port. And it almost certainly will encounter such a port unless it escapes to the side.

Calculate the size of the active surface. Since it acts as the "hypotenuse" of a right triangle, one of the calculations of its surface area will not be a or b, but c, and since c=sqrt(a2+b2) it will be LARGER in area than a flat hood.

Lastly, the hood may, in theory at least, act upon the plume over a far greater time domain than the flat plate hood, which is fairly digital (plume impacts, what happens happens)

Here, the whole plume falls under the flow influence of the hood surface at an earlier time, since the rear can be set lower than a plate hood. All impacts that are not immediately sucked into an intake port "duct" themselves up along the slanted plate until they hit, you got it, another intake port!

Yes, some will get past the top lip. But I would be willing to bet that the slanted plate is NOT the worst design. There are, in fact, SEVERAL "worse" designs. And if we have any readers on here who happen to have a slanted hood and would like to have a "suck off" to see just how good the angled design is in contrast with the flat plate, I would just LOVE to work on a demo.


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RE: Angled hood

@mojavean: wow, I'm in awe. And, your points are indeed well taken.

First: I cannot for the life of me get my old Photobucket account working. For the record, here's my fashion equivalent to the Futuro hood (AKA Form over Function):

boots

At any rate, there are a few quibbles I'd have with your logic. First, I do agree in great part with your arguments. For the simulations, as you have drawn them, I believe much is correct. I'd throw in a couple thoughts though.

First, your assumption that plume is in contact with angled hood for longer time because of the increased length (your hypotenuse) of the hood does not account for the potential acceleration of plume flow rate due to upwards angling of plate. In other words, in the flat plate model, while there is loss of effluent off the edges of the plate, in general, and especially towards the center of the plate, the natural tendency of the hot plume to rise vertically will tend to keep the effluent "bouncing" off the horizontal plate, thus increasing the capture time in which the fan can evacuate. Against an angled plate, the tendency of plume to rise will tend to accelerate the effluent up and over the edge of the plate. Agree that a very high flow slot at the top edge would be critical, but I still wonder if the acceleration effects of angling will outweigh the channeling effect to the slot. Plus, the longer the effluent travels along the plate, the more is lost off the edges to the left and right.

My biggest issue is that you have not really modeled the Futuro Diamond Wall hood correctly, and I believe even you'll agree with me on this. The actual depth of this hood is only 16''! That means that the upper, outer edge of the plate extends barely past the middle of, say, a Bluestar RNB304. That means, using your model, that essentially ALL off the effluent from the front three burners will be uncollected.

If the hood actually projected at least 30'' out from the wall, I might have to concede on your points. But neither of us would advocate a hood that only vents the back burners. That's truly a hood for show, not go. And count me in on the LBD, and out on the high heeled hiking boots.


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RE: Angled hood

I'm totally not getting into it about the hood. Re Mojavean's LBD, however, while I agree that the cited "optimal" outfit of "sturdy shoes, comfy trousers, a loose shirt and a hoodie," is probably the one that is most adaptable to any environment, especially outdoors, the pictured dress looks pretty comfortable, and for where the weather is hot and shelter is abundant (i.e, out of direct sunlight), and heavy physical work (the kind where you get scratched up) isn't called for, it would be the preferable, practical clothing choice, allowing for unfettered movement and plenty of air. :) Whereas, I didn't get to see Clinsrega's LBD, but that boot is patently ridiculous on all fronts, and only has "warm" and "trendy" to recommend it under any circumstance I can imagine. I think the metaphor are getting a little dense. :)


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RE: Angled hood

LOL! Love that boot! Clinresga! Though the pic links were broken, I did click through anyway and found your album that included what must be the penultimate range and hood "alcove" setup. If that is your kitchen it is truly lovely, though I would not call it the LBD; it's more like an exquisite ballgown.

I had not actually looked at the dimensions of the hood in question, but if the protrusion is only to mid range then I complete concede that point. My theory requires that most of the plume at some point make contact with the hood surface.

One other detraction to my early observation I neglected to mention was that in exchange for the longer time domain under the influence of the hood, those cooking surfaces below the high end of the ramp would have more opportunity to plume outward, out toward the cook and out to the sides. So there's that.

I do see and agree with your point that the momentary "bounce" might induce more entrainment, but it is something I would like to experiment with first. Gas behavior in turbulence isn't always intuitive.

One quibble. I do not think under normal circumstance you will see any acceleration of the gaseous exhaust. If anything, as it gets further from the heat and begins to cool the density per unit volume will increase, slowing as it rises. Exception would be effluent molecules approaching a port connected to the exhaust aperture. They would become entrained in the faster-moving air currents heading out of the room via the fan and would thus accelerate.

But for this thought experiment, I assumed a constant plume 'velocity' of 1m/sec which I simply borrowed from Kas who knows about such things.

Fun discussion! Now I am going to go see if I can look up the actual specs of some of these hoods before making an ever bigger fool of myself!


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RE: Litte Black Dress

Plllog, that was pretty much my point when I used the LBD illustration. Under some circumstances that ensemble may prove ideal. Those circumstances will not include climbing Mt. Whitney or going to the dog park to do cartwheels; fine!

Not every kitchen or cook will require perfect entrainment of cooking fumes. Some of us can get by okay with lighter, more avant-garde approaches, deliberately trading some capability for style. If the buyer understands the potential tradeoffs, all is well in ventland.


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RE: Angled hood

Many older houses have no kitchen ventilation *at all*, or just a fan set in the wall behind the stove. They "get by okay."

I could understand saying we don't cook much, we don't own a wok, we don't sear meat etc., and so we'll just spend a couple hundred on an entry-level Broan hood and "get by." But the OP proposes spending $1700 on something that's not going to do any better job -- so that's something like $1500 for bling alone.

If you want blingy conspicuous consumption, there are plenty of ways to do it (e.g. fancy granite) that don't detract from the functionality of your kitchen. What's unfortunate is when the bling harms the functionality, which is why the boot that cripples its wearer was a really smart analogy.


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RE: Angled hood

@mojavean: no fool you. Discussion was fun, and really thoughtful. And the metaphor was the some of the best entertainment I had all day. Keep the deep thinking up, it's what GW is best at. Nowhere else in the world can people obsess over something as seemingly mundane as a vent hood.

@colin: pretty much my thoughts. But, I have a soft spot for pure bling at some times, in some places. And there is validity in a kitchen that's purely a design statement. I just think it's important for folks who make that choice to realize that discussions of performance are really not relevant.


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RE: Angled hood

Oh, okay, Mojavean, I misunderstood your point. The thing about that particular dress is that it is more functional than your climb Mt. Whitney, cartwheels in the dog poop (eeeeew!!! Aerials in the dog park maybe...). I'd rather do housework in your LBD than the hiking clothes, though I agree that if the only outfit you have is the hiking one, it's the most adaptable and practical.

Here's impractical bling for you, only good for one purpose. :)

hello dress

So maybe the hood in question, which isn't entirely useless would be more like this?

gown

It's beautiful, hard to sit in, hard to walk in, but impressive, and you could put on an apron and do the dishes if you had to...

The thing about something that is supposed to be a functional object, like a hood, is that, unlike Clinresga's high heeled hiking boot, it isn't supposed to just look like it does the job, but act like it. The argument some make that they never have all the burners going at once, etc., etc., as Colin alluded to, so just get a 600 cfm hood with a decent catchment over a CC because there's no money left for more, and it's not really necessary... I get that one. I don't get spending big bucks to remove function from a functional item, however, even if there are never searing steaks and stinky fishes... Especially, because the one unlooked for time when all the burners are going and all the smellies are cooking will be when there is company to impress, who instead of admiring the hood, will be wondering why it doesn't work better.

In other words, I agree with y'all about the boots and the hood, just think you didn't reach far enough on the gown. [Big Wink!] ;)


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RE: Angled hood

ROTFL!

Clin: Happy to have you as my interpreter.

Mojavean: I think that generically your points are well taken. Specifically, besides the hood depth from the wall issue, covered above, I have one other quibble. Conservation of momentum applies to the rising effluent whenever other forces do not act on it. When the plume hits the bare metal where there is no significant air flow to do work on it, it will tend to reflect such that the angle of reflection relative to the normal to the surface equals the angle of incidence, just a photons do when hitting a mirror. This directs the plume down and/or outward, depending on the hood angle. However, other rising effluent may interact with this reflected plume and entrain it in more of an upwards direction. It will depend on what burners are doing what. I would guess that Schlieren photography would show curling of the plume at the impact zone, with the curls rising upward and outward.

Otherwise, I believe your argument is consistent with a point I have made before: One can have two out of three of economy, effectiveness, and aesthetics.

A point I didn't notice addressed above is that the slot area of this design appears to be very small, and pulling a high flow rate through the slots might cause more noise than the more common baffles generate with the same flow rate.

kas


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RE: Angled hood

kas: should have kept my mouth shut and let you give the definitive answer. Still like my hiking boot analogy, though.


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RE: Angled hood

I fear your publicizing them will have dear consequences for the ankles of the fashionistas.


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RE: Angled hood

Might make hiking more fun for the guys though.


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