Follow-up on Wolf noise level: the showroom Wolf models I saw had working lights but not working fans, so I wasn't able to hear them in person. The salesman told me that Wolf baffles aren't as tight together as the BlueStar's, resulting in lower noise overall for the Wolf. I have seen a few negative reviews for noise with Broan hoods, and Wolf uses Broan motors, so I am wondering about the possibility of using a Fantech motor (the motor of choice for Modern-Aire) instead. I think it is much easier to mix and match blowers when using an external application than an internal, but perhaps someone more knowledgeable can advise.

External blower choices will be greater than internal choices because the blower has to mate somehow with the hood interior. A Brand X blower probably won't be designed to mate with a Brand Y hood. Also be sure that the hood blower control's assumed motor type is the same.

Narrower baffles will probably be better at lower specific flow rates (cfm/sq. ft. of baffle) than wider baffles that will have a higher minimal flow rate to achieve good centrifugal extraction, but noise will be higher with narrow baffles for the same specific flow rate. A 300 CFM rated blower in a largish hood (meaning probably 200 CFM with no deliberate MUA) might be too low for large baffles to even work well; mesh may be better in that case so long as the mesh filters are kept clean.

Ideally, if limited by a specific maximum specific flow rate, the fan curve should be more vertical at the full flow (r.h.) side of the graph so that when restricted, more air flow is achieved. This may not be compatible with typical hood blowers, with desirable low blade tip turbulence noise, stable operation (no hunting), etc. A close-wall blade fitting axial fan might work, but I haven't looked any up as no one would probably want to experiment. A question for Fantech, perhaps.

@kaseki Thanks for the reliable advice which will save me hours of more research. So, we'll just stick with the Wolf internal blower to make sure it mates up with the Wolf hood. If I restrict my criteria to mesh filters, then I am back to models that don't have capture area -- in other words, hoods where the underside is flat or nearly so. I could certainly find mesh with a capture area in a higher CFM, but after weeks of looking, I'm only seeing a handful of suppliers that even make an concave hood under 400 CFM, and all of them have baffles.

I didn't measure the width of the baffles on BlueStar vs. Wolf. To my memory, they weren't appreciably different in size. The showroom salesman said it was how "tight" the BlueStar baffles are aligned that creates the whistling noise. He said the Wolf baffles are "set further apart."

@kaseki So here's a question if you might have time to offer further advice. My range is 30". I wanted to go with a wider 36"x24"x18" Wolf pyramid wall canopy hood with baffle filters. Given the 300 CFM restriction, might I achieve better centrifugal extraction if I went down to a 30" hood, based on your comment above?

Side note: I live in a temperate climate and can open a window year round when the fan is on high, plus my home is far from airtight, so I don't think the lack of MUA will restrict my actual CFM by a full 1/3. I'm also planning to mount the hood at 30" above the range.

Can you tell us what brand(s) you have for your other appliances? Might help with recommending additional options.

Thank you, Sabrina. We have:

• GE 30" range/oven combo in black
• Kenmore refrigerator in black
• Frigidaire dishwasher in stainless steel
• New sink for the renovation will be stainless steel

We are concerned about scratches in getting a surface-painted black hood, and Broan is the only manufacturer that has a through-color black hood where the color is mixed with the stainless steel, but it has a flat underside and only comes in 30'' width so we crossed it off.

I'd rather have performance over beauty since at the moment I can set off a fire alarm just cooking a couple of hamburger patties. We need a ducted hood with a capture area given our 400 CFM or less restriction. I would love to know if I've missed something, but I've spent about a month looking at several dozen brands and can't find much outside of BlueStar, Wolf or an expensive custom order that meets the criteria. I'd like to stay under $3K for the hood. The range/oven itself cost only a few hundred dollars.

By the way, this renovation was unplanned. We had a first-floor water leak that rushed ahead all this research and planning, and the overall repair and renovation budget is already high, so this is far from our only budgeted purchase. Thanks so much for everyone's advice.

@kaseki I'd still be interested to know if you think going down to a 30" instead of 36" hood at a low CFM would aid with the centrifugal extraction. See my comment above Sabrina's with more details. Thanks!

Inspo Inspo wrote: "Given the 300 CFM restriction, might I achieve better centrifugal extraction if I went down to a 30" hood, based on your comment above?"

If the same flow rate is applied to a smaller aperture hood, then the flow velocity will be higher, and centrifugal extraction will be better. However....let's start at the beginning.

The primary functions of a hood and associated ventilation system are two: capture and containment. Capture is best when the hood aperture overlaps the cooking zone, so a 36-inch wide hood will help with that. Containment requires that the flow rate per square foot of hood be high enough to assure that the hottest rising plumes (cooking dependent) get through the baffles without reflecting out of the hood (partly baffle dependent, hood shape dependent, and mainly cooking dependent). Note that neither of these is related to grease capture by baffles. Baffles, besides providing a fire stop, are intended to keep down grease build-up in the duct.

Residential systems are a long way (unless you cook all day) from commercial systems, so the grease build-up in the duct will be modest, even with imperfect baffle operation. At best, baffles only collect the larger particles from the grease particle spectrum. If I were you, I would aim for the larger canopy to keep down grease getting into the kitchen and let the baffle performance be whatever it is.

Aim to achieve 1000 ft/min air flow velocity in the duct by correct duct sizing. This will minimize condensation and impingement collection in the duct.

Thanks so much, kaseki. It's frustrating when you think about the fact that probably a lot of homeowners across the country without any MUA system are going out and buying the more powerful hoods and installing them in their kitchens oblivious to the code or perhaps in defiance of it. If I could only get up to 600 CFM, my hood options would be essentially unrestricted and include dozens of new options. I appreciate your help so much. We'll go with the 36" then and probably have to keep it at 300 CFM since we are already lined up for a building inspection on it post-installation.

Follow-up on BlueStar baffle angles: one of the showroom hoods I saw had a nice slant and containment area to the hood. The other had a much shallower slant. This is concerning, especially since the BlueStar website isn't clear as to which models have the larger containment area and which don't.

Also, when I've mentioned "capture" in comments above, I should have said "containment." Capture is related to aperture, or the size of the opening underneath the hood. Containment has more to do with the height of the cavity inside that is capable of holding effluent until it can be exhausted. Some professional hoods have a flat underside with no containment area. Wolf has a nice containment cavity in its pro hoods.

Actually, containment more properly refers to permanently moving the cooking effluent to the exhaust duct side of the baffles and thence out of the kitchen space. I would include the under-hood volume as a component of the capture process. (If you trap a lion but he easily escapes it may be fair to argue that capture wasn't achieved.)

Baffle slant aids transfer of grease to a storage container in commercial hoods, which require the slant angle to be at least 45 degrees. This requirement hasn't been extended to residential hoods. At residential slant angles, the grease from modest cooking will likely solidify (rancidify) on the baffles before it would travel to a collection point.

If there were no safety risk, no one in the code enforcement business would care about MUA. The reason it wasn't an issue until roughly this decade was (a) few combustion appliances were available with low velocity/low temperature exhaust and (b) the insanity of sealing up houses to inadvertently trap potentially harmful chemicals inside hadn't been popularized.

@kaseki I am continually amazed at your thorough grasp of everything related to home air quality and exhaust. You must design hoods for a living?

Thanks for the clarification on "capture." That's interesting that residential hoods don't need any slant to the baffles. A showroom sales person pointed out to me that Wolf residential hoods don't have a grease tray at the bottom of the baffles which are slanted at least 45 degrees with that brand because you aren't going to be doing so much cooking at home that you'll need that before you clean the grease off the baffles themselves. Here's the catch with non-slanted residential baffles, however -- the flat baffles leave no under-hood room for capture beyond maybe 1 inch of height provided by the surrounding lip. When I see a hood with a flat underside, I am also seeing a hood that has essentially no room for capturing any extra bursts of effluent that may outpace my blower, but if a high capture area isn't necessary for a residential hood, then I may have a few more brand options open up to me.

I can see the concern for MUA in modern homes. In our home, we don't have any other appliances that generate chemicals in the living space area that could be disturbed by an exhaust fan, to my knowledge. We do have a fireplace that gets used three or four times per winter for atmosphere. The home was built in 1985 and isn't airtight by any means.

Regardless of our circumstances, we will have to stay within a 400 CFM code requirement for now. Do you think I could go with flat baffles on the underside, or is gaining a capture area such as afforded by the slant in Wolf hoods valuable? The Wolf hood we are looking at comes in at just under $3K, and I know my husband would like to knock off the extra thousand we could save by going with a less expensive brand while at the same time he's willing to put out the money for the Wolf if that's going to be the most effective. I've set off fire alarms with our old hood just making hamburgers, so we want to go with something as capable as possible for the renovation.

I have not in the past nor present had any employment related to HVAC. I am, however, an engineer. When I started my (dear wife's) kitchen renovation process in 2007, I was appalled by the lack of available technical information, apparent lack of use of engineering principles, and sometimes lack of fabrication quality of the many hoods presented at showrooms or touted on-line. In my view, leading this charge of dubious devices was Vent-a-Hood with their "magic lung" claims. There seemed to be no science connected with the subject.

There was, of course, HVAC science and engineering, but it seemed to be either hidden or second hand for residential hoods; all of the reported work was performed for commercial hoods. Commercial cooking HVAC manufacturing sources, engineering communities such as ASHRAE, and government entities such as the California Air Resources Board, had performed studies that could, with a little extrapolation, be applied to the residential kitchen application space. All that was needed was to research what was out there and apply the principles to establishing the requirements for a residential hood system.

From functional and performance requirements come construction requirements, or at minimum a means of sorting among proffered systems. Recognition that affordability, performance, and aesthetics were not simultaneously achievable became apparent, as were the restrictions imposed by an existing house architecture on viable approaches.

At the time, this had to be done while employed and dealing with the myriad other system engineering details of a revised kitchen and related house changes, so this process was abbreviated by necessity. It was also abbreviated by having to make leap-of-faith extrapolations due to the poor state of component specifications. (I was aided by Wolf engineering providing fan curves combined with hood and duct pressure loss curves that I could at least generalize from.) Additional information was published as time passed and included in what one might consider to be my gestalt of cooking plumes vs. getting rid of them.

In the 10 years or so that have passed since then, my impression is that there has been an unexpected (by me) drift of devices and principles from commercial ventilation into the residential kitchen ventilation space, particularly on the MUA systems front. I think that there has been an improvement in hood quality, or at least in the appearance of functionality at the lower price end of the hardware spectrum. Even VaH seems to have improved, at least providing some technical information and perhaps downplaying their use of magic.

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I think flat (horizontal) baffles with little capture volume underneath can work, but only if one can achieve the specific flow rate needed for immediate containment of the portions of the plumes reaching the baffle space. (Note that in this case it is the baffle space that needs to overlap the plumes, not the (absent) entry aperture.) Often In commercial hoods the baffle area is relatively small -- one row only -- but the large and tall hood has high angle sloping sides leading to the baffle assemblies so that plume reflections are upward. In such cases, one might need 180 CFM/sq. ft. of baffle space to match the potential plume velocity.

My experience and that of Greenheck for commercial cooking suggests 90 CFM/sq.ft. of entry aperture, but if induction cooking is the heat source, and the pans are not used for High temperature grilling and wok cooking, a lower value may be sufficient -- 50 CFM/sq.ft. perhaps.

But you are limited by the flow rate, and flush horizontal baffle hoods that will overlap the pan area with the baffles may be hard to find.

Consider a minimal hood system solution over induction. The blower has to be rated at 400 CFM max. Allocate 40% to pressure losses and call the actual flow 240 CFM. At 50 CFM/sq. ft., you could have an entry aperture of nearly 5 sq. ft. This is 36 inches by 20 inches, so heavier plume cooking should be performed at the rear hobs. Higher temperature smokey or greasy cooking may partially escape this system, but lower temperature grease plumes, such as from slow-cooking bacon, should be captured and contained.

My choice would be to go with a hood embodying desired performance properties in size, shape, and interior configuration, and buy a sub 401 CFM minimal blower compatible with it. This will meet the inspection requirements if not the performance requirements. When time permits consideration of a more powerful blower and some MUA adaptation can be made.

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There are many MUA approaches that might be sufficient for a modest air flow rate upgrade, particularly where there doesn't exist a combustion appliance back-draft hazard that your code doesn't seem to take into account with any relief. Except in the case of unmodifiable condos and apartments, there should be an MUA scheme that can be adapted beyond opening a window. It may be simpler than you presently surmise.

Suppose for example that you wanted to upgrade to an 800 CFM rated blower. Again we assume a 40% pressure loss (it will actually be different, depending on myriad factors), and consider that the first 400 (240) CFM was free, MUA-wise. So there is 240 CFM additional MUA that needs to get into the house and perhaps be heated. A six-inch duct with damper into the basement or brought to a register or diffuser somewhere in the house, or even tied into an existing air heating system could be considered.

Heating would depend on outside temperature, but for this air flow "trifle" only 5 to 15 kBTUh would be needed. This could be achieved with a 1.5 to 4.5 kW space heater. The existing furnace might be sufficient.

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On my ca. 2007 Wolf Pro Island hood, there are minimalist trays at the lower ends of the slanted baffles. These do collect some grease over long periods of time. I don't know if they are included by Wolf in present "Pro" hoods.

Thanks for the fascinating background on how you became such an expert on ventilation. We all at Houzz appreciate your continued participation in advising especially since your remodel was a decade ago. I believe I'm heading this morning to go purchase the discounted Wolf floor model hood based on all our discussions. Then, I'll purchase the blower later after I think more about the MUA suggestions you provided. It's possible we could actually add an MUA vent along the interior ceiling of our kitchen to the wall and cover it with a soffit. I like the quote, ". . . Particularly where there doesn't exist a combustion appliance back-draft hazard that your code doesn't seem to take into account with any relief. . . ." We had even discussed talking to the inspector about this and seeing if we could get up to 600 CFM given our circumstances. We live in a really small suburb of a major city, and code does exist but seems really lax when it comes to the inspections we've had done thus far.

Even with zero hazard, some MUA improvement will be needed as the desired hood flow rate is increased in order to avoid choking the hood. We just don't need to worry about exactly what the resulting house differential pressure will be.

This is a great thread. In my brief reading. Specs aside, couple of other things that are critical to a hood. Duct layout - aka, in a typical 8-10 foot ceiling, where one mounts the hood higher at around 6 feet AFF off the floor, , and if not going with a remote blower, but it's a short vertical run and then angle, it creates backpressure.

I'll have to take another deep dive into the post, but hood design as well. Even see some hoods where the controls or the light housings/bezels, lightbulbs are filty as these are generally in the front *where one normally uses the front burners*, and the intake of air is being drawn from these places.

It is worth pointing out, I think, that the pressure differential across the blower, called pressure loss, is essentially the same whether the blower is in the hood, at the end of the duct outside, or in a door blowing into an otherwise sealed house. The pressure loss is the sum of all the losses due to friction and turbulence in the duct, duct cap where present, hood transitions, baffles, make-up air system restrictions, etc. Any slight differences in pressure loss with blower position will be due to local transitions where the blower is mounted versus the blower's air flow uniformity at the blower exit. The resulting flow rate will be that which applies to that pressure loss on the fan curve plot.

Front of hood deposited grease is due to insufficient overlap and/or insufficient air velocity at the hood aperture. Hoods are generally poor at drawing air from the vicinity of the burners. Most plume capture depends on the plume's upward velocity, mainly driven by the buoyancy of hot grease and water vapor and air. The plume naturally expands as it rises, hence hood aperture overlap is desirable.

What is the installed distance from stove to hood do ya'll have urs. Our hood bottom is around 6 feet off the floor. If I recall the recommend design specs , it was calling for a ridiculous low height of 3 1/2 feet from the stove (if I recall it correctly)

My hood is around 31 inches from the top of the range to the bottom of the hood. Specs recommended 30 inches.

I've seen hood mounting heights recommended at 66" to 72" above the finished floor (AFF). Sometimes the range itself will specify what height the hood should be, but those measurements are sometimes way too low, and you have to counterbalance the advantage of greater extraction capability with a low hood versus mounting the hood a bit higher to avoid injuring your eyes or head on it. Some styles of hoods come with pre-set duct cover heights so you only have a couple of choices if you use the factory cover.

We're hoping to build out a little from the upper wall to mount our new 36" x 24" hood further out over the burners in hopes of catching more of the effluent from the front burners.

The hood should have installation instructions and specify the height the hood should be from the top of the stove top to the bottom of hood for best performance. The range will also have a distance listed. For our VAH the height specified was 30 inches from stove top to hood bottom for best performance and the bluestar range had minimum clearance of 30 inches.

Ok finally rhe lightbulb illuminated in my dim brain upon reading Kaseki’s post, second one up - the long one. Huge thanks for your time. i am not an engineer - a field of science yes but barely passed trigonometry and physics so my eyes just glaze over with all of the sine waves, cosine waves etc etc and various engineering calculations ….😅 i am learning though. We are also trying to ‘engineer’ our new kitchen replacement to be as healthy as possible, With so far little help from the local ’professionals’ but hoping to make a connection at some point. My dear husband is an electrical administrator/engineer and around his crazy work schedule is doing his own in depth research to retrofit MUA and ventillarion into our old log house to accomodate our new kitchen and high BTU Blue Star range. it is a bit overwhelming to say the least but we are so appreciative of what we have learned from this board.