Need feedback re Wolf hood sizes and 2 cfm motors

10 years ago

After reading these forums for weeks I've decided to purchase a Wolf 30', All Gas (R304) range and a 30' Wolf Pro vent hood (under cabinet). The hood installation will require removal of an existing over range MW (with recirculating fan) and the new duct work will run straight out the back as the hood will be mounted on an exterior wall.

I'm bounded on the hood width at 30" but have a choice between 10" tall, 22" deep, 500 cfm (internal blower)...or one 18" tall, 24" deep with either 600cfm or 900cfm internal blower. The 24" tall cabinet above the hood will be compromised with either selection but aesthetically I think the 10" tall hood will look better and leave me a usable, albeit, shorter cabinet space above the hood. However, I've read enough on these boards to have me leaning heavily toward the 18" tall hood because it offers the 24" depth and I'm willing to live with the slightly more 'boxy' look and 4-5" (basically unusable) space left over for the practical gain in surface area. Lastly, I should note that I'm 6'5" so I'm having the hood mounted at 36" above counter surface (max height).

So...can anyone present a strong argument to go with the 10" high hood? If 18" tall hood is the obvious practical choice, does the blower cfm choice (600 vs 900) make a big difference given the range underneath and kitchen setup? I believe these hoods are manufactured by Wolf these days (internal parts sourced elsewhere, I'm sure). With that, any thoughts on whether the often cited suggestion that a higher cfm blower will provide a more quiet operation (at similar lower output) and is that a enough of a reason to go with higher cfm?

Any/all feedback is much appreciated.

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Comments (3)

julieste
10 years ago
I'm in your shoes as far as looking for a hood for my 30" Wolf R304, and we are looking to buy in the next few days. Our R304 has been installed since February (it replaced an older JennAir downdraft), and we haven't had any ventilation at all since then other than opening a window. We are not big into frying or woking and only occasionally do stinky food. In reality there have only been a couple of times we have even felt we needed a hood. Plus, for the most part, we only have two burners going at a time on top. Heat from the oven exhausting is an issue, and since it got hot out we have been using our electric wall oven rather than the gas Wolf so as not to heat up the kitchen too much. We live in a cold climate, so the extra heat output from the range is nice in the colder months.

Our primary goal will be to have a hood to remove hot air expelled by the range in the summer heat. In the past four months there have only been max a half a dozen times when we needed to open the window specifically to deal with cooking fumes or output or smoke. And, the wall and cupboard area by the range are not showing any evidence of a lot of grease coating them.

So for all of these reasons, and because we have a ton of constraints as far as hood size, we plan to go with something smaller than either option you are discussing. On our short list of hoods the largest hood we are considering is probably smaller than the smaller one you discuss. Having lived with this range already for months we are comfortable with this decision. We know it will work for us. What is best for you and your cooking style may be another story.

I too have read everything here for ages now and have come to an understanding that what is recommended here as maximal is often for an unconstrained situation in a kitchen gut or in new construction where everything can be planned around the absolutely optimal hood that will take care of a range with all four burners and the oven blazing away at the same time.

Many of us who are doing minor remodelings or just appliance upgrades do not have the luxury of following all of that advice.

Good luck with your decision. Whether I gave you a compelling argument to go with the 10" I don't know.
kaseki
10 years ago
The first requirement is for the hood aperture to overlap the rising and expanding thermal plume containing the grease effluent. If you don't generate grease vapors, then the hood rules may be different.

The second requirement is for the flow rate maintain an adequate velocity at the hood aperture (and the baffles or mesh filter) to ensure that the captured plume is contained. This means that the local velocity at a point where air moves through the filter should equal the plume velocity (up to three feet per second). Because baffles and meshes partially fill the space they occupy, it seems that hoods work OK with perhaps half that velocity at the aperture, leading to a requirement for about 90 cfm per square foot. Note that the velocity is partly driven by total BTU, so the Finnish papers on this subject (referenced at my Clippings) should be consulted for particular cases.

The third requirement is to have a fan/blower that can move the required cfm at the pressure loss that the ducting, hood transitions, baffles, and restricted make-up air have.

The fourth requirement is to have a duct diameter that keeps the flow velocity up so grease not captured by the filter doesn't stick to the ducting, this is about 1000 ft/min.

The fifth requirement is adequate make-up air.

The sixth requirement is to not hit one's head on the hood, so it should be placed where that won't happen. Higher means a need for larger aperture for capture, so the cfm will have to rise. And one is back to the first requirement.

kas
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Ideally, you start with enough aperture to capture the rising expanding effluent. Then, having the aperture defined, calculate the CFM necessary to achieve a velocity equal to the rising effluent velocity. This would require 180 CFM per square foot of aperture for 3 ft/s rising effluent if there weren't other considerations. One of those is that with baffles, that velocity only needs to be achieved over about half the area due to the aero shape of the baffles and the flow around them. I didn't figure this out from computational fluid dynamics, but from the behavior of my Wolf Pro Island hood dealing with my induction wok which is offset towards one side (the induction cooktop is offset toward the other side). I expect mesh filters to behave similarly due to the mesh blocking at least half the area of the filter. While a fairly poor analog, if one thinks of the effluent as billiard balls in a zero gravity field hitting the hood filter, one can appreciate that conservation of momentum will cause those hitting a flat surface to bounce away from it such that the angle of exit equals the mirror image of the angle of arrival relative to the perpendicular to the surface that the effluent hits (just like light). The need is to change the momentum of the reflection by entraining the effluent into the hood air flow. Ideally, this is done as the effluent reaches the baffles/mesh and there is little bouncing reflection going on. You may appreciate that the flat surfaces of your nominal hood where there is no mesh will be regions where there will be effluent reflection. Some of that will be captured by the air flow which pulls in from a range of angles. In any case, for best operation, one wants the actual hood aperture to encompass all of the rising effluent and not make the aperture smaller just to get the local air velocity up. (A commercial kitchen hood is an example what is relatively optimal for maximizing capture while minimizing the cost of air handling.) But the bigger the hood, the more CFM needed, and the more make-up air CFM that has to replace the air in the kitchen. This not only adds the modest cost of ducting in MUA, but significant cost if the MUA has to be pushed by a fan and the fan has to be controlled to keep the house pressure in a narrow range. This can be more complex in some ways than large commercial buildings which can run MUA continuously and use pressure differential across a damper to control whether the fan output just circulates around in the fan loop or is pushed into the building. I think my previous post suggested that for the hood aperture you have, the actual CFM achieved will probably be enough. But imperfect capture and containment should expected from the hood aperture design due to the flat areas not being capture areas. kas
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There seems to be a trend on this forum that CFM requirements are strictly related to hood size, height and BTU of the cooking surface. While those are all important factors in the equation the bottom line is that no one can give a totally accurate response with out seeing your home. What is the diameter of your exhaust? How long is the run? How many turns in the run? There is a significant loss of CFM for every 90 degree turn or even a bend in the exhaust. A qualified installer should be able to help you factor your CFM requirement after they inspect your home and determine the requirements of your exhaust vent. Once that is done you can look at the information you have acquired and make an informed decision. We currently have 600 CFM over a smaller range than the OP is considering. I would want to start at 900 CFM for a 36" range and then consider the other factors that will affect the actual CFM before deciding if that is enough. Every home is going to be different even if ranges and hoods were equal.
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It would be best to start any quest involving kitchen ventilation to study the literature, or at least study the many many threads here on the topic. I would prefer to write answers to questions that are based on my possibly inadequate previous writing than generate yet another long message covering the entire topic. You may wish to start with the "Hood FAQ" which can be found by searching. I believe it is listed under @opaone. Hoods are about capture and containment, and success in this depends on many factors, the most critical of which is sufficient air flow velocity at the hood entry to ensure that which is captured is contained and expelled from the residence. This velocity is independent of how many burners are running at once, but rather what the cooking surface temperature is plus plume heat augmentation by gas burners. In any case, the 100 CFM per 1000 BTUh is derived from certain standardized commercial hoods, not residential hoods. See the Greenheck Guide available at https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf for comparison between the 100 CFM per rule of thumb and the hood aperture velocity rule. I suggest 90 CFM per square foot of hood entry aperture, and this aperture needs to be large enough to overlap the rising and expanding cooking plumes. Let me adjust the salesman's statement: "...because the design pulls more air than a filtered/baffled hood of the same [zero static pressure rated] cfm [when hanging unattached to anything in free air]." Ventahood use squirrel-cage blowers that also perform the function of baffle filters, thereby eliminating that cause of pressure loss. However, as blowers go, they are more susceptible to other pressure losses than conventional blowers, and hence if there is extensive ducting, or inadequate MUA, their flow rate will be less than the actual rate asserted. My guess is that you should have a 24 x 42 inch hood aperture, requiring an actual 630 CFM obtained from a 900 - 1000 CFM rated blower. Read MUA related threads to determine how closely the interior air pressure has to match the exterior air pressure for safety. Your state may require heated MUA. There are a lot of ways to accomplish MUA under these conditions, and the threads here should help you understand what you have to tell us to allow better tailored help. kas
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Differential means the difference between the outside temperature and the temperature you want the MUA to be (warmer or colder than outside). CFM means actual hood CFM, and the actual hood CFM will never exceed that provided by all the sources of MUA CFM available at the kitchen. If the differential pressure is zero, then one has perfect MUA (pressure balance) and the hood will only be "gagged" by its own baffles, transitions, and ducting. The achieved indoor-outdoor differential pressure won't generally be zero, but it can be kept modest relative to changes on the fan curve. Aim for 90 hood CFM per square foot of hood intake aperture. This should provide complete containment for most cooking for captured plumes using residential hoods with baffles. (Plumes are initially captured if the hood aperture overlaps them.) So, for a desired/required 800 CFM, say, one finds 800 on the abscissa and goes up to a differential temperature curve representative of an outdoor and indoor temperature difference, and thence left to the ordinate where the BTU/hr needed is listed, based on the specific heat of air and the mass of air being moved at that CFM. BTU/hr has a counterpart watts value for electric heating, and also a tons of air conditioning value if one intends to cool. Conversion factors may be found by use of an Internet search engine.
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mdrei
Original Author
10 years ago
Kaseki...you are like the GW fluidics professor and your feedback is valuable. Thanks for the education.

Needinfo...thanks for your thoughts. You've given me more to think about. I've noticed the parallels in our status (and purchases) based on your previous posts. We also don't fry foods on a daily basis but venting all odors and grease is my objective with this hood. Kaseki's points are noteworthy given the boundaries of retrofitting an existing kitchen and the height at which I'll mount this hood. MUA isn't a factor, as far as I can tell, since I don't have any other gas appliances (someone correct me if I'm misguided on that assumption). Vent power will be important, at 36" off the surface of the range (and the constraints of the surface area), for the times when I do sear something or fry fish and switching to a back burner isn't desirable to me. I don't want to overspend but I don't want regrets 6 months down the road, either. I also know there are options at a fraction of the cost but functionality and quality are my priorities. Decisions, decisions...

Need feedback re Wolf hood sizes and 2 cfm motors

Comments (3)

julieste

kaseki

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mdrei
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Need feedback re Wolf hood sizes and 2 cfm motors

Comments (3)

julieste

kaseki

Related Discussions

mdreiOriginal Author

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

mdrei
Original Author