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Help with hood selection.

Posted by rph123 (My Page) on
Sat, Nov 9, 13 at 9:34

I have purchased my rangetop for my new house, now I have to decide on a hood. The rangetop I purchased is the Wolf srt364clp. It is the 36" with 4 burners and charbroiler. I know I need a pretty powerful hood because of the charbroiler, probably at least 900cfm from what I have read. My hood will be made by my cabinet maker so it needs to be an insert. Any suggestions? Do I need to stick with wolf on the hood also? Thanks.


Follow-Up Postings:

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RE: Help with hood selection.

One other thing, how high above the rangetop should the hood be?


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RE: Help with hood selection.

For the first question, I can only say that you don't have to stick with Wolf, but I am not aware of any reason why you shouldn't other than possible cost or your cabinet design needs a custom insert size.

For the second question, typical distances are 30 to 36 inches. Higher requires a larger aperture to collect the rising effluent that expands as it rises. Lower may affect sight-lines to pots at the back, and/or head bumping, depending on your height. I recommend construction of a side-view stick-figure drawing that allows you to see what happens as the stick figure bends at the waist to evaluate potential head bumping. The drawing can also be used to determine sight line blockage, if any.

I have a Wolf Island hood operating at 34 inches above the surface of my induction cooktop.

Don't forget that a 900 cfm hood will draw less when attached to ducting, and much less if sufficient make-up air into the kitchen is not provided.

kas


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RE: Help with hood selection.

In kitchen renovation about six years ago installed hood approximately 4 1/2 feet over cooktop. You can put it as high as you want with the caveat that the higher you go the more draw you need.

To reduce noise we have the motor & fan on the exit point, not at the hood. Makes it quieter. Hoods can get expensive but don't need to be. My opinion is this should be the cheapest item of renovation as it is lowest tech. If it is recessed under cabinet no one needs to know it isn't an expensive brand of duct ornament.

Brand we used is Best. Has down lights and controls at counter level since hood is out of reach for wife. Has grease filters that run through dishwasher. No complaints.

One consideration, our hood has so much draw we have to be careful when there's a fire in the fireplace; on full it'll pull smoke into the house. Design flaw on my part. A bit lower would've required less draw.


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RE: Help with hood selection.

Avoiding back-drafting combustion appliances, and back-drafting fireplaces, is one reason for the need for make-up air (MUA). The other is to get the flow that was expected from the hood.

Hood collection of cooking effluent is mainly driven by the effluent up-rising velocity and the overlap of the hood with the expanding cone of effluent. To keep the captured effluent captured, the actual flow rate at the hood should be high enough, over the entire aperture, to keep the rising effluent (which has momentum) from "reflecting" out of the hood. This flow rate is in the region of 1.5 ft/s [not m/s] times the aperture area for baffled hoods, probably similar for mesh filtered hoods.

Because the air velocity away from the aperture due to the hood fan, whether to the sides or down at the cooktop is so slight relative to the rate at the aperture, increasing flow rate with height is only useful (beyond general house ventilation) if the aperture grows as it should to capture the rising and expanding effluent.

kas

This post was edited by kaseki on Sun, Nov 17, 13 at 8:26


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RE: Help with hood selection.

Kaseki:

In the interests of science performed 3 pot boil to attempt to confirm/refute the well-reasoned expanding cone hypothesis. With variable speed fan tried to take photo evidence of performance at different speeds. Unfortunately, my skills as a videographer/photograher were not up to the task. However, it seemed to me that fan speed did _not_ materially impact the quantity of steam that initially escaped, as you predicted.


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RE: Help with hood selection.

I think I made a typo above; it should have read 1.5 ft/s.

Generally, Schlieren photography is needed to view the hot gasses. Schlieren photography can image changes in the index of refraction of air due to heat. Examples may be found on the web. Steam from boiling water will not be as hot as the air rising from a griddle or frypan.

The cone angle depends on various factors, and for more [a lot more] information, review the two papers by the Finnish authors listed in my My Clippings.

kas


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RE: Help with hood selection.

Kaseki:

Skimmed through those & bigger article that discussed hood sizing & ventilation for commercial applications. Thanks. Got me thinking that current design might be modified, & I don't have to create as much draw even if I don't change hood.

However, was wondering to what extent these studies are focused too much on heat as proxy for particulate. Heat management is important in a commercial/industrial setting, but for a single induction cooktop it's not really the issue to be managed. The other is to what extent a hood that's flush or near flush with the ceiling creates a special case for study.


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RE: Help with hood selection.

In the second part of the "Finnish" series of experiments, the heat experiments of the first part were replaced by cooking experiments, as I recall.

The hood for a Bunsen burner and for an array of wok hobs may be physically different, but the principles that they should be designed against are pretty much the same.

Restaurant kitchen hoods are typically 7 ft. up, whereas residential kitchen hoods are 6 ft up, so the restaurant hoods should be larger relative to the cooking surface than for residences.

It is true that hot gas from gas burners adds to the effluent that induction doesn't have, but depending on what is cooked there can still be a lot of hot effluent, particularly when using a griddle or wok. I believe at least one of the cooking devices in the "Finnish" study was an electric griddle, which should provide an analogue of the fry pan/griddle/wok case when using induction.

For some commercial kitchens, larger arrays of hoods are used, and even perforated ceiling systems (with interior intense UV to break up the grease before it gets to the outside). These may not be practical for even the most fanatical of us.

kas


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