"With all due respect, @bry911, "financial consequences" is not logically equal to "financial harm" or "more ... than they can afford."'

What?! A deception that causes someone to spend more money than they otherwise would is financial harm. I don't know why you decided to add "more... than they can afford."

Furthermore, a negative financial consequence based on an exaggeration is financial harm. Are you suggesting that a reasonable person wouldn't foresee someone canceling a purchase agreement when told they are going to get sicker while living there?

You are assuming a deception, which is an active measure not the same as believing something that you don't believe, or even believing something generally understood to be untrue. I don't think expressing an opinion here rises to the level of tortuous interference.

The "more ..." phrase was copy-pasted from what I believe was your writing farther above, with removal of some text shown by the ellipses. Strangely (or perhaps not since Houzz absorbed and deleted an entire message insertion of mine earlier today), I can't find it now, even with a search tool.

@kaseki - I really am not interested in the semantics discussion. Whether the statements are intentional exaggerations or misunderstandings, they remain despite the critique.

@opaone  I'm in Paris right now and noticed a vent hood setup that doesn't look like a vent hood because of the way the kitchen is constructed, but it has some aspects of a commercial vent hood in terms of large capture area and large containment area.  The photos should be self-explanatory.
Bill

That's very cool. Functionally they should have some sides to it so that it's like 140cm wide rather than 5,000cm wide :-) Great idea though.

I always wonder about these slotted-edge types whether trying to pull the required air flow plus plumes through the slots doesn't lead to significant noise relative to more typical baffle designs. And what is actually inside past the slots for filtering/fire stopping?

@kaseki I'll have to check whether this is a slotted intake or whether this exhaust panel drops down to open up the aperture.

Here's another view, below.  I agree that sidewalls up above would be good, bit maybe it acts as a really big capture and containment area as long as the cooking effluent stay up there (which I would doubt...)

Billy

Good catch on the slotted. I'd missed that. Be interesting to see if it does drop down. Either way I think a standard baffle is a better option.

I found out it does not drop down.   I think the slotted is part of a baffle system.  They use a commercial restaurant blower on the roof.

Pondering the same as @kaseki was pondering...

Each of the slots in the baffles for our hood are about 3"x1/2" so maybe about 1in² each? Times 60 = 60in². Or... 60" of 1" wide slot? 90" of 3/4" wide slot?

@opaone I assume this a true baffle array where each \_/ under baffle is covered by the same shape inverted and offset. I imagine it would have to be to perform the fire stop function.

Obviously, baffle area is very small in the photo. In order for the hood to function there would have to be high velocity flow through those slots. Nowadays with CFD available, I suppose a lot of non-intuitive configurations can be made that are effective.

I would have expected, for a commercial sourced hood, for the baffles to look more this this Flame Gard example.

They do have a standard baffle as you describe that is lower static pressure and quieter. These are a bit better at grease/particulate extraction.

Aha! Bafflement no more. There is more than meets the eye. Thanks.

@opaone

Here you go:
https://www.greenbuildingadvisor.com/article/study-explores-methane-leaks-in-gas-ranges

Useful perhaps for indoor air quality discussion. When compared to exterior environments, the article lacks comparison to methane venting from all the tectonic rifts and fractures, undersea and on land, volcanic and earthquake related, and tundra melting methane release.

It is a weak argument to compare to CO2 effects, because, as Hanson said upon retiring, the models aren't working. This is likely because CO2 lines don't broaden with concentration (see quantum mechanics), and their insulating performance in-band is almost total already. This makes the ratio of methane effects to CO2 effects potentially extremely large, but in an absolute sense the predicted change in global temperature for the predicted additional methane release needs to be expressly asserted, else the author should have stayed away from climate comments.

Until the climate models can address clouds, and the generation of clouds from the water droplet nucleating effects of cosmic rays and solar CMEs, and the regulating effects of clouds on the earth's albedo as a function of increasing evaporation with temperature, one should maintain some level of suspicion about claimed atmospheric behavior due to gas concentrations. Modelers have recently publicly asserted that they need 1000X present computer power to properly deal with clouds.

P.S. Houzz a propos threw this link up on the r.h. side: https://www.houzz.com/discussions/887462/what-do-you-think-about-this-design-with-elica-twin-rangehood

@billy_g, thanks for posting that. I'll have to read the report later but one thought... Scott's article is without context and perspective which are both critical. Discussions of gas and induction should also include the other for comparison. Just saying that gas is bad isn't useful because induction may be just as bad or worse in other ways. Unfortunately we don't know that yet.

We also have to have perspective with regard to cooking effluent. Is the harm in gas effluent huge compared to that of cooking, about even, or a rounding error? I don't think we know. Or at least know as well as I'd like to know.

And then there's perspective to everyting else. What about other gas appliances in the house? And other sources of reduced air quality? Is the methane from the range significant or insignificant? That said, I'm a low hanging fruit fan so if I can easily remedy something rather insignificant and see some IAQ or other improvement I'm all for it.

As for me today... I prefer the monster I know and know how to deal with (gas) to the one I don't and so can't know how to deal with (induction). I do have countertop induction hobs that I use though.

I agree with you kaseki and opponents.

The article was more interesting for its discussion of effluent than for the dribble about banning gas stoves.  Instead of banning hot showers because of the negative effects of high humidity and condensation inside a structure code often requires ventilation which makes more sense in the case of every type of stove or cook top, including gas.

I meant opaone...  spellcheck changed it to "opponents!"

This is all so much information and far more than I had any idea even existed when we began planning our kichen remodel. I am glad that we are learning about the importance of the various facets of kitchen ventilation now, but it has thrown a peoverbial wrench into our planning as our old house is not going to be easy to retrofit. I did try to start a thread specific to our situation but I think I posted in the wrong place and it was too long, hence I will try again with effort to be more succinct! 😅

Sometimes it is akin to throwing the proverbial Caterpillar D9 into the sandbox; wiggle room becomes very slight.

Try copying the misplaced message into a new thread within the Appliance Forum. Leading off with a summary for skimmers may be helpful, but too little information will just lead to several comments requesting more that take up just as much space.

"This is all so much information and far more than I had any idea even existed when we began planning our kichen remodel."

Yes. And realisticallly too much for most people. The bulk of it is in response to various questions/comments people have had over time so it does add up. I'd like to one day cut it down a chunk and/or move a lot of stuff to Part II.

It is all worthwhile info and it certainly needs to be better addressed in home building and remodeling.

Hi all - I have been doing research on range hoods for the past few weeks and never knew how much went into choosing a good one that did the job it was intended to do. We are in the midst of a kitchen remodel so I don't have the luxury of building the perfect range hood set up but I want to do the best I can in the area I have. That being said, after reading a lot on this site, it seems to me that a few commenters [ @opaone & @kaseki in particular] have a lot of knowledge about the subject and I was hoping that either of you might be able to give me some advice. I am now thoroughly on the commercial range hood bandwagon and read that @opaone had an Accurex installed in their kitchen. I have been speaking with an Accurex rep in my town now but have hit a brick wall regarding the dimensions I need. I was wondering what the dimensions of the Accurex were that @opaone had installed as I recall seeing someone mention that they were 60"L x 30"W x 30"H. If that is correct, do you also have LED lights and a baffle? I do have a 48" range so I wanted to install a 48"L x 30"W x 30"H. My rep just informed me that LED lights and a baffle required 39"W hood minimum for a wall canopy hood and I really don't want to install one that wide in my kitchen as my space is very limited for a hood.

I would appreciate any advice or clarification. If Accurex is not possible in my situation does anyone have another commercial hood company that they could recommend?

TIA!

First, it would be good to have introduced this question in a new thread, rather than in a FAQ.

Second, it would be good to ensure that you and Accurex are using the term 'width' to mean the same thing. Sometimes it means what I understand your question to refer to as 'length.'

Generally, a wall hood needs to be wide (long) enough and 'deep' (wide) enough (front-to-back) to capture the rising and expanding cooking plumes under the conditions of the kitchen. This includes cross drafts and turbulence from human motion. If the hood base is at seven feet, as most commercial hoods are, then this forces a wider and deeper hood to be used for (more or less) full capture than for residential use where 30 - 36 inch base height above the cooktop is standard.

So if you are dealing with a 24 x 48-inch range, then the wall hood entry aperture (may include some of the light bar) for 7-foot height should be in the range of 30 x 60. To get that from Wolf, for example, one would need to use one of their "outdoor" models. I don't know anything about those models' guts, so I can't comment on interior suitability.

In commercial hoods, I'm sure that 30 (or a bit more for lights) x 60 is within the scope of construction. Commercial hoods typically use lights in the center area, rather than angled from the front edge, so perhaps this is why Accurex is at 39 inches. @opaone will know more, and may grace us with a comment soon.

A few photos are below...

Looks like a good adaptation of a basic commercial configuration to your application.

Yep - thanks for all your advice on hood design considerations and airflow and more over the years!

Thank you @kaseki and @billy_g for your helpful comments and suggestions! I am really impressed with the hood that you designed and had built @billy_g. I have a couple of questions for you relating to that. Did you install a MUA system? And where did you get the removable grease cup? Is that something that can be ordered online?

Yes, you can get a grease cup from restaurant supply houses or on Amazon: Commercial Kitchen Restaurant Duty Canopy Hood Grease Cup- Removable Keyhole Mount 4” Deep (Large Capacity Grease Cup) https://a.co/d/cZ7VbzU

Thanks! I might end up having my GC get his metal fabricator to build a hood for me as well using your drawing but I noticed that there's a note that says See drawing re angled part for baffles. Is this a separate drawing that you can include as well or is it just referring to the angled part that you have drawn to hold the baffles?

Here you go:

Thank you so much for all your help! Have you been able to use your hood yet?

@billy_g, nice job! What baffles are you using? (Edit: Just noticed the note on your drawing that I missed earlier).

@ksanchez9 I have not used the hood yet but I like listening to it! Gas for the cooktop will be connected next week.

@opaone thank you for compiling the relevant information and sharing your experience and journey with your hood. This was key!

@billy_g hopefully, you've had good success with your hood now that your gas should be connected. How is the 1400 cfm blower working? Do you think you could have gone with a smaller one? I am still trying to locate a company to build one for me but I think that I might have some leads. I did have one more question about where you located the switches for your light and fan as I didn't notice them on your drawings.

We're not moved into the house yet (long story) so I don't have an update on the blower. I suspect you could go with a lower CFM blower for a 42" hood (and 36" high BTU cooktop).

I located the switches on the kitchen backsplash - not ideal but not a problem, and in this case better than mounting them in the hood and blocking the airflow. You also could mount the electrical junction box in a wall cabinet and have the controls under the cabinet but that's kind of awkward...

Reminder: Residential hoods with sparse reservoir volume below the baffles need air velocity across the entire entry aperture for the highest velocity plume cooking (up to 1.2 m/s), whereas with Commercial hoods having large reservoir volume below the baffles, the hood averages the plumes and can generally get away with lower average air velocity. So @opaone can sear or wok on a burner and get away with lower CFM with his quasi commercial hood than I can with my Wolf Pro Island hood. If he is searing on all burners, however, the total plume CFM (sum of plume diameters at hood entry times plume velocities at hood entry) is the minimum flow rate he has to use, which will be approximately the same as I have to use (90 CFM/sq. ft. = 90 ft/min) even when I am operating only one hob.

See the table from the Greenheck Guide below. I operate at the "Medium" flow rate for hot oil cooking, where Opaone can usually operate at the "Light" flow rate. This relation is true proportionately when cooking with lesser plume loads. [Click image to expand.]

https://www.tagengineering.ca/wp-content/uploads/2015/02/KVSApplDesign_catalog.pdf

This relation, however, doesn't continue to near zero plume velocity (e.g., cilantro watching). The commercial hood at 7 ft height is more susceptible to cross drafts and at very low plume velocities may well have to operate at a slightly higher CFM than the residential hood at 6 ft. depending on the conditions. In any case, minimum operational CFM is likely driven by baffle grease extraction requirements than capture and containment of low velocity odors.

@billy_g this looks like a fantastic solution, and I'm thinking I might borrow your drawings (and parts suggestions) to see if I can find a fabricator willing to build something similar. Definitely do post updates on your project!

One complication for my kitchen, I think I'll need the duct to open from the rear rather than the top. It's a direct 10" round duct that just goes horizontally right outside near the top an 8' ceiling. I think ducting from the top would require placing it too low, unless I were to do a version with a lot less height (but then the baffle angle would probably have to change). I'd be doing an external blower on the outside wall of the house. Given that the duct is otherwise very short and free of bends, does anyone think rear ducting would negatively impact the performance of this design?

I currently have an Elica over which performs pretty poorly over a 30" Capital range, and I've been mulling over what to do about it for almost a year now.

It shouldn't be a problem to duct from the rear. It would lower the noise if you have a bend rather than a straight duct run... is there room for a duct silencer in the straight run?

I’m pretty sure there isn’t room radially, but also the “run” is less than a foot. I think it at least shouldn’t be worse than my current setup, an internal blower with fixed settings that can’t run lower than a (claimed) 300 CFM? Unless the box would create some sort of resonance that amplifies the noise or something.

But I’m also hoping high containment volume would allow most everyday range use to work well running below “300”, as in the “light” column in kaseki’s chart above.

Ah, I see. Your goals make sense to me.

Maybe @kaseki can chime in with his thoughts.

For additional context, I had for a while been considering the Prestige High Capacity hood that was discussed in another thread some months ago (since it actually is deeper than other residential hoods and has a design that avoids wasting capture area space on a front light bar as most do), but I’ve been hesitating because it’s still not quite what I want and would either be a bit too high in my kitchen if rear ducted or mounted at a head-bonking height given it’s depth if top ducted. Whereas this solution seems like it would be way more performant, and I could get the height right.

Booonnngggg. I prefer the gong over chimes for a wake-up call.

Not sure which thoughts need to be expressed, but I will note that the airflow requirement that I usually recommend -- 90 ft/min = 90 CFM/sq. ft. (see Greenheck method "Medium" column in Fig. 4 in an earlier message above) -- is based partly on the medium column value (note that Greenheck's values are for commercial hoods with gigantic reservoir volumes below the baffles, not residential hoods with barely any) and the idea that good entrainment of the rising plume effluent should be achieved if the baffle gap air velocity is commensurate with the maximum plume velocity (3 to 4 ft/s). So my recommendation is for residential hoods performing "Light" column tasks.

If the user intends something extravagant for interior cooking, such as operating a char broiler, then significantly higher air flow is likely needed, and it may not be possible to fully collect the plume without a more commercial-style hood configuration.

At the low end of the air flow regime, flow rates for minimum rising plumes should not be below the speed that allows the baffles to centrifugally extract grease, or below the speed that ensures that flow into the baffles is not easily disturbed by barely noticeable turbulence or drafts. This is likely why the Wolf control in my hood has a minimum flow rate.

@opaone I have read all of your posts and comments... thank you for being so informative on this topic! On a sidenote: I happen to follow your designer and builder separately on instagram and have pinned many photos from your house as inspiration for our new build. I went to your Wordpress site for the exhaust hood FAQ's and realized that it is in fact YOUR house! What a neat moment! It is beautiful.

A few questions re: hoods.

1) I am waiting on a reply from our local Accurex reps re: doing a 42"x30" residential hood for a 36" gas range (either Viking 5 Series or Bluestar RCS)...its been a few days and nothing, so I'm trying to formulate another path forward. In lieue of Accurex, my backup is the Wolf Pro Wall Hood which seems to be cautiously recommended by @kaseki as the best residential option at a 42"x27" depth mounted at 36" above our range (upper maximum in their specs--I am a tall person). I mainly make mac n cheese and scrambled eggs for our kids... any high heat cooking I will plan on doing on the back center burner(?)... I don't think I ever use more than 2-3 burners at once and even that's pretty rare .... knowing our lifestyle / cooking needs... does this seem like an adequate compromise?

I don't want to throw almost $3k down the drain over a completely inferior solution, but I'm not doing anything that elaborate in the kitchen. (Also if there's a cheaper option, please share!). I looked at Prestige, but their website gives me the impression that they are out-of-business / not reliable.

2) We are building a home in New Hampshire... I know your house is in Minnesota. Our builder is advocating a 6" duct mainly for insulation purposes. He is fine going larger, but has warned us that insulation and cool air seeping back into the kitchen is a potential tradeoff. The specs for the Wolf require a 10" duct. Is our hood going to become a vehicle for ice cold drafts during our Northern winters? Any thoughts around countering this potential issue?

3) New Hampshire building code is 400CFM before requiring makeup air. We have been told we don't need makeup air... some reasons being: our house is very large (4600 sq. feet) and very open. We have high ceilings (10'). And like you, we insisted on a wood-burning fireplace, because there is nothing better on a cold winter night than a wood-burning fire... but with that will come more drafty air into our house. Due to the "capture area" of our 42x27" hood, can we stay within the 400 CFM range, avoid makeup air, and still have good indoor air quality.

Follow-on to this question. It sounds like ideally we would want to do an inline blower, however the minimum Wolf has is a 600CFM option. My understanding is that a 600CFM inline blower is not actually operating at that capacity. Is there a way to calculate it's actual operating capacity (i.e. would it be under the 400CFM code threshold).

I will push for makeup air if it is irrevocably necessary (and it sounds like it is virtually always advocated for by you and @kaseki). I'm just wondering if any of the specific factors to our build and lifestyle are relevant.

Thank you in advance for any feedback you can share!

Well, I live in NH, and can provide some climate-relevant comments, at least if you live south of, say, Plymouth.

I should note that my Wolf hood (actually built by Independent for Wolf in ca. 2008) is a 'Pro Island' model hood. I believe all of the Wolf hoods that are of the canopy type -- wall and island -- will be suitable for cooking ventilation if large enough and provided with sufficient flow rate. I have no other styles of Wolf hood to directly evaluate.

For those who have reached this point via tl;dr, a brief summary follows without much justification. First, it is necessary to determine requirements and then select among candidate hood systems that meet those requirements.

• For capture of rising and expanding cooking plumes, the canopy has to overlap the plumes at the height of the canopy. For 36-in hood base hight over the counter, this is about 3 inches wider than the cooktop, as well as deeper.
• For containment of hot cooking -- defined here as hot oils at the smoke point, searing, wok cooking, and other combined moisture/grease plume producing cooking -- an air velocity at the hood base of about 90 ft/min is desirable with residential style canopy hoods with small volumes in the reservoir space below the baffles. This directly implies 90 CFM/sq. ft.
• Typical blowers in typical pressure loss operating conditions will likely move only about 2/3 of their rated (zero static pressure) flow rate.
• So, take the intake area, multiply by 90, further multiply by 1.5, and the result should be in the ballpark of the required rated blower flow rate (CFM). This is likely to be higher than 400 CFM. Cooking content, induction vs. gas, and other factors may allow some reduction of the calculated requirement, while poor MUA can increase the rated requirement, but I wouldn't drop very much if you want to ensure clean interior air and no grease on the house surfaces.
• Duct size should limit full power air flow to between 1000 and 2000 ft/min.
• No air is removed from the kitchen that isn't resupplied. Insufficient supply just causes the blower to move less air. The resupply is called make-up air (MUA), and it can be deliberate or accidental (through the walls, say). Deliberate MUA can be passive (no blower) or active (with blower). Accidental is undesirable for many reasons, and just because there is a limit at 400 rated CFM doesn't mean MUA should be ignored.
• How well the MUA needs to keep the kitchen pressure close to that of the exterior air depends on presence or not of combustion appliances that can be back-drafted at some household pressure. Back-drafting is hazardous.

So by example 42 x 27 is 7.9 sq. ft. calling for about 700 actual CFM and around a 1000 CFM rated blower. In a 10-inch duct, 700 CFM has a velocity of 1200 ft/min, so I would not go smaller.

Also, please note that with a roof damper and a damper above the hood, minimal cold air will be drawn into the house when the blower is off.

I space allows, a silencer (Fantech LD-10 for example) can be placed between hood and blower for a considerable reduction in noise.

If you use passive MUA because of lack of combustion appliances, you will not be able to run the fireplace when the blower is operating at higher flow rates. For this an active MUA is needed, such as Fantech makes.

_________

P.S. A house as large as the Pentagon would eventually drop in pressure with an externally vented hood unless air was replaced. House size doesn't matter except for providing more leakage paths that you should avoid using.

P.P.S. Wolf answers their phones and provides technical data. Otherwise, they are one of no doubt many suppliers of quality hoods that can provide good capture and containment when properly specified. For example, I strongly suspect that ModernAire knows what they are doing, even though I have never seen one of their hoods in person. Similarly, ABBAKA, to name two.

Thank you @kaseki ! I did not realize you were in NH too, this is very exciting!

I have the Wolf pro wall hood earmarked for its 27" depth (https://www.subzero-wolf.com/wolf/range-hood/42-inch-pro-wall-hood-27-inch-depth), and it sounds like "best practices" means I need makeup air :)

Re: your point: "For containment of hot cooking -- defined here as hot oils at the smoke point, searing, wok cooking, and other combined moisture/grease plume producing cooking -- an air velocity at the hood base of about 90 ft/min is desirable with residential style canopy hoods with small volumes in the reservoir space below the baffles. This directly implies 90 CFM/sq. ft."

I will virtually never be cooking hot oils at their smoke point :) Is there a CFM rule of thumb for boiling water, etc?

Last question, regarding the the 1000 CFM blower. I am under the impression there is some CFM loss depending on the location of the blower? Is the 1000 CFM rec for internal, inline, or remote? (or maybe my premise is incorrect). Thank you!

Last question first. We can model a blower (motor, fan, housing, etc.) as a device that is ducted from output to a point of resistance and then back to the input. Real ducts have losses (friction, turbulence, etc.), hood baffles have losses (change flow direction twice), and transitions such as in the hood have losses. WE call these pressure drops "pressure loss." It is the loss around the loop from cooktop to outdoors to indoors at the cooktop that add up to the total pressure loss. To first approximation, it doesn't matter where in the loop the losses are, and correspondingly, it doesn't matter whether the blower is in hood, in duct, or at a house boundary. In reality, different blower types may be differently sensitive to duct effects close to the blower, so position relative to an elbow, say, might have an effect. Also one might have one of each type with the same zero static pressure rating, but with different fan curves relating flow to pressure loss. Other than using good design practices, these anomalies should be accounted for by the 1.5X factor I introduced above.

If you are generating pure steam, only activities such as boiling down maple syrup would likely over humidify the house, but in any case, if the steam upward velocity is much less than 4 ft/s, then a lower value than 90 ft/min may be sufficient.

However, normal cooking entrains more than water into the plume, and these components can leave residue on surfaces, along with odors. Poaching fish might not require a very high air velocity for containment, but you certainly don't want to fail capture, which can be influenced by air flow rate. A low velocity plume might also be a somewhat spreading plume, particularly when turbulence from human movement and drafts interfere with the rising plume.

The only other consideration that occurs to me at the moment is resale where a hood functional for the full gamut of residential cooking is usually desirable.

Thank you @kaseki this all makes sense, I appreciate you taking the time to respond to these and tailor your answers for those of us that are less engineering-minded!