thank you for the responses!

Thinking out loud...

One thought that occurred to me is that a hood that is lower (and that is also effective in capturing, containing and exhausting effluent) may be better for the cook from a health standpoint than a larger one that is overhead.

A larger overhead hood may be pulling a lot of effluent by the cooks face on its way to being exhausted. While this hood may do a better job overall and result in healthier indoor air quality in the house it may not do so well by the cook.

A smaller consumer hood (24" or less depth to wall) mounted lower may result in less effluent at the cooks face. We know that with most or all consumer hoods a lot of effluent does not get captured (and what is not captured is not contained nor exhausted) and will bypass the hood and this effluent will most likely go by the cooks face.

The question is which is likely to result in more effluent by the cooks face?

I would argue, assuming that the cook lives in the house and has no relevant respiratory illnesses, that the question should be: Which design provides the lowest effluent inhalation by the cook over some extended period not less than 24 hours. Perhaps the question should be extended to: Which design provides the lowest effluent inhalation by the house's occupants over some extended period not less than 24 hours.

In my view, @opaone, your approach wins. That said, it should be worthwhile to architect the hood guts so that there tends to be air passing the cook from outside the cooking zone rather than effluent rising past his face while being pulled toward the outside edge of the hood. At the very least it would be more comfortable.

Exceptions can be imagined such as: If the exterior air replacing the hood draw via the MUA system is contaminated in some way that is difficult to filter at MUA flow rate scales, maybe cooking effluent would be preferable (so long as cleaning grease from walls doesn't defeat the entire argument).

Containment is industry standard terminology. As explained to me by engineers the process is:

Capture - For the most part this is the size of the bottom opening where effluent first enters the hood. Effluent that does not enter the hood, that is not captured, will generally spread out in the room/house space unless there is a secondary exhaust system.

Contain - This is simply a bunch of open space to contain effluent until it can be exhausted - a holding space. The effluent from cooking is often very bursty so, in CFM terms, perhaps 100 CFM for a minute and then a burst of 5,000 CFM for a few seconds (when something is flipped, etc.). Even a 1,200 CFM blower cannot keep up with a 5,000 CFM burst. So, lacking sufficient containment area, the excess effluent rolls out from under the hood and in to the room. Quit often the majority of effluent is contained in these short bursts, not in the effluent produced between bursts.

Exhaust - The blower exhausts the contained effluent.

Higher CFM's mostly cannot make up for too small a capture area (aperture). Hot effluent that's rising is not easily controllable and it takes an enormous amount of airflow to change its trajectory enough to pull it in to capture it. If it's not captured it can't be exhausted.

Higher CFM's have a better chance against lack of containment. A 2,400 CFM blower (assuming it actually achieves that) may be able to get 70% of the excess left by a 1,200 CFM blower leaving only 30% to roll out in to the room. But that's a still big, expensive, loud, costly to operate blower (and duct system). This is why better hoods are designed with a large containment area because then the blower need only keep up with the average effluent over time rather than try to keep up with the bursts.

This is why a commercial hood with a large containment area (and why all commercial hoods have large containment areas) can perform better running at a silent 300 CFM than a consumer hood running at 1200 CFM. The 300 CFM blower need only keep up with the average effluent over time. The 1200 CFM blower is exhausting 90% fresh air much of the time and then when a burst comes can only exhaust 20% of it while the other 80% goes out in to the room.

Hope this helps.

Good point on breathing effluent over time. I wonder from a health standpoint how X amount breathed in over a short period but at higher concentrations compares to the same X amount over 24 hours but much lower concentrations.

Response to @opaone

Ultimately, containment requires that the plume become entrained in the airflow passing into the baffle slots. It cannot indefinitely stay in the containment area/capture volume. This is why I argue for an overall blower air velocity (at the hood entry aperture) that is sufficient for the velocity at the baffles to be equal or greater than the plume velocity. A small diameter fast plume could reflect out of the hood even if the hood CFM were significantly higher than the plume CFM. Reflection, of course, depends on conservation of momentum and the new direction (possibly downish) has to compete with the uprising blower induced airflow, thereby making a second attempt by the hood system to achieve containment much easier. In my view, it is this factor that weights the hood design toward enough capture volume (containment area if you wish) to allow recapture and containment of any reflected plume components.

If I recall, the highest plume velocity recorded in the "Finnish" study was 1.2 m/s, or about 4 ft/s (240 ft/min) at the plume center. For an expanded plume from a large wok assumed to be 2 ft in diameter at the baffles, (part of which is gas combustion products), the three square feet of plume (much of which is actually at a lower velocity per the published plume velocity profile, but assumed here to be at 240 ft/min) is a flow of 720 CFM. I can't imagine a residential cooking condition, at least one that I would likely be part of, that could generate a transient 5000 CFM burst.

Further, a 2-second burst at 5000 CFM is 167 cubic feet in volume. There are no residential hoods that I'm aware of that have that much 'containment area.' Your quasi commercial hood may have such a volume, and I gladly acclaim more [cooking] power to you for acquiring it. I just don't see it as a requirement for most people, even those grilling or wok cooking.

A dual commercial wok cooktop with knee control and 100k to 200k BTUh per burner may well achieve 5000 CFM of transient plume, but I believe that much of that transient is due to the sudden increase in combustion products from the cook's control of the burners, and not something that can be generated by the wok contents.

I concede that your containment definition is consistent with at least one reference I just looked at: Improving Commercial Kitchen Ventilation System Performance, Design Guide 2 – Optimizing Makeup Air – Updated 03.15.04; possibly accessible as CKV_Design_Guide_2_031504.pdf. (See following extract.) While the definition of containment agrees with yours, the volume in question is named 'reservoir.' *

"The phrase "hood capture and containment" is defined in ASTM F-1704 Standard Test Method for the Performance of Commercial Kitchen Ventilation Systems as "the ability of the hood to capture and contain grease-laden cooking vapors, convective heat and other products of cooking processes.” Hood capture refers to these products entering the hood reservoir from the area under the hood, while containment refers to these products staying in the hood reservoir and not spilling out into the adjacent space." (c) 2002 by the California Energy Commission.

______________

* The larger study from which this blurb was taken is MAKEUP AIR EFFECTS ON

COMMERCIAL KITCHEN EXHAUST SYSTEM PERFORMANCE, potentially accessible as: 2003-04-10_500-03-007F.PDF

We did the final blower door test on our house yesterday and also tested several bath exhaust systems. Our range hood measured 992 CFM on max (and 53.6 dB(a)). The guys doing the work said that they had NEVER had a consumer range hood do better than 50% of rated max and most, including VAH, usually came in about 30% of max. So when there are comments about fan curves, duct design and static pressure this is the effect.

For those interested this was measured by turning the hood on full and then cranking up the blower on the blower door to achieve as close to 0" pa (adjusted for natural indoor pressure) as possible. For fun we also did this for several of the bath exhausts that we also measured with TEC Exhaust Fan Flow Meter. More to come.

@kaseki, for the 90cfm/sqft of aperture, what is the containment volume for that?

Short answer: I've never seen a report parametrically linking containment volume to recommended flow velocity (equivalent to CFM/sq. ft).

Originally, I was thinking 3 ft/s for a plume average (180 ft/min) and a slot to area ratio of 0.5 for a baffle space. Hence 90 ft/min across the aperture (ignoring various non-baffle framework elements) implies 180 ft/min into the baffles. I think it was later that I noticed Greenheck suggesting 85 ft/min for the "medium" class of cooking levels. Note that these are recommendations for commercial hoods with, as you never let us forget, large capture/containment volumes (reservoirs). My Wolf Pro Island hood has modest (at best) reservoir volume and so immediate containment past the baffles is needed.* As it turns out (not final) I have at least 100 ft/min (without any other household blowers running) and induction wok cooking and induction stove top searing are easily contained.

My engineering instinct is to design to assure desired results under adverse conditions and this may also influence my recommendation. So far as I know, no one has complained on this forum of inadequate ventilation when designing to this hood intake velocity.

I wouldn't be surprised if you found that 50 ft/min was adequate for almost anything you did under your hood short of moving a 100k BTUh wok hob into position under it.

______

* If you would like, @opaone, I am willing to measure and roughly calculate the actual containment volume of my hood. Because this hood is the longest of the Pro Island hoods, there is somewhat more volume per transient cooking event than a shorter hood would provide because more sideways spreading is available than from a hood sized for just one 36-inch cooktop.

I am both incredibly appreciative for all of this information, and overwhelmed by it. I have a few questions to help me understand:

1. If I am understanding correctly, the 36"x27.5" range I plan to buy requires a hood that is 3-12" deeper AND wider than that? That seems huge. It would extend way out into the kitchen in the front. Am I understanding correctly?

2. How do I calculate the 90 CFM per sf of aperture? I think that for a hood with a ventilation area of 36x27 I would need a CFM of at least 607.5 to have a 90 CFM per sf. ((36/12)x(27/12)) x 90 = 607.5. Correct or no?

3. What professional has the right skills to asses the "tightness" of my home? An HVAC tech? Or should the contractor for my remodel be able to do that?

4. How can I tell if I want my duct to go straight to the outside vs have a turn? I see that sometimes a turn is actually better, but how would I know that?

5. My design plan calls for a custom wood hood cover. Something like this photo. Is this a bad idea for any reason?

Florida Historic Renovation · More Info

It may help to know that I rarely cook on the stovetop (maybe once every two weeks), and I bake even more rarely (probably only 10-12 times a year). I'm really just going with a 36" range for aesthetics and resale. So after reading all this, I'm kind of thinking if I get a hood with the 90 CFM/sf with dimensions that match the size of my range top I should probably be ok. I'm assuming I may need a heated MUA because I live in the Northeaat. House is about 45 yrs old, with no noticeable drafts but given the age I don't think it's supertight.

Thank you for any advice you can give. I can't tell you how much I appreciate the time and thoroughness you both have provided here!

1. Your hood needs to be 42" wide by at least 24" deep up to as deep as the stove but not beyond. Are you deepening the base cabinetry to match your stove depth? You sure could preserve some cash just going with a 30" range and 36" vent hood since you are an infrequent chef. I don't think it would hit your resale value. Plenty of high-end stoves come in 30" widths.
2. Most blowers for a stove of 36" in width will be at least 600 CFM up to over 1000 CFM (sometimes up to 1600 CFM) with a variable speed control. Some experts have written about the idea that a lower CFM is really all that is needed if a robust positive airflow can be maintained (see next point), but it also depends a lot on whether you plan to sear steak or boil eggs, so the basis of your calculation should account for more that just a straight square foot to CFM formula.
3. You will need a makeup air system for a stove and vent hood this large to meet both jurisdictional requirements if you live in city limits and also for mere safety. The house tightness or not doesn't matter when you get over 400 CFM with your blower, but being in a cold winter climate your house is probably already fairly tight. If you selected a 30" stove you could get away with a 300 cfm blower and not require heated makeup air which can be a big drain on your energy bill. Check your jurisdiction's requirements, because some cold climate areas limit CFM more than others without makeup air. A powerful vent hood can empty your house of existing air in under an hour.
4. Straight vs bent depends a lot on noise level and where you want the blower placed. Straight is better for extraction and lower noise for an in-hood blower, but if you are installing an inline or exterior blower, you can more easily get away with a bend.
5. Wood hoods can catch fire from powerful range tops. You will need to follow the stove's specifications for how far away from the burners combustible material can be. This limits your ability to place the distance of the hood closer to the effluent for maximum efficiency.

One remark to the above comment no. (3): "A powerful vent hood can empty your house of existing air in under an hour." Vent hood blowers can rarely flow any air when the pressure in the house falls more than 2 inches of water column relative to outside pressure. Since the absolute pressure is around 34 feet of water column, this is a fairly tiny drop. If there is excellent MUA, then the powerful blower can refresh house air at 60 x the blower's actual baffle-limited CFM per hour, but it dilutes the air exponentially, so if you fill your house with smoke, expect a few of those time periods for clearing. During that period, the grease and soot will be settling on all surfaces.

W.r.t. (2): The principle that the required CFM depends on cooking is correct, as it is proportional to the plume velocity that is to be captured and contained. However, if the plan is dominated not by cooking but by reselling, the follow-on owners might be informed enough to know whether the hood ventilation system is adequate for their cooking or not. Hence, I would aim for adequacy from the beginning.

To lwfromny: The actual hood overlap requirement is to overlap the rising and expanding effluent plumes at the height chosen for the hood. An angle of 10 degrees from vertical measured from the locus of pan edges that might be used should be satisfactory. Note that pan edges rarely exceed the stove top dimensions, but on the other hand, the tangent of 10 degrees times 36 inches is about 6 inches. So at that height, one needs to decide on hood size vs. burner chosen for the greasiest activity. Also, side cabinets can (positively) influence the flow pattern, as will cross drafts (negatively).

The number one purpose of MUA is safety w.r.t. combustion appliances. I would not depend on the 400 CFM rule for safety. Either give them their own MUA, which is usually available as an add-on, or their physical space its own MUA, or be sure that you don't lower the house pressure where they are below their negative pressure ratings (maybe as low as -0.03 inches, w.c.) by providing enough passive or active MUA. This may require someone making a measurement for you.

I wouldn't worry about duct turns so much as having enough blower to deal with the baffle pressure loss, the overall duct loss, and the MUA pressure loss (if any) given the hood system's blower's fan curve (loss of flow with pressure loss). A duct into an attic and thence to the roof will often allow space for a silencer, which will greatly quiet the blower noise at the hood when at full speed.

Many other searchable hood and MUA threads here will further your understanding of these points.

It is best to start a new thread for a new project, as this thread is/was supposed to condense the subject matter into a FAQ format. Unfortunately, I haven't had time to play editor and organize it.

Thank you so much to both of you 😊. I think I do have some more questions - will start a new thread if I do.

[Putting this bit about using flush ceiling registers for venting here for eventual inclusion in a reorganized FAQ.]

I think the following requirements are important, in no particular order:

• Ceiling joist revision must be practicable and structurally sound.
• Make-up air must not short out the plume path to the vent aperture. To introduce the MUA, use another room, hall, the kitchen floor, several toe kicks, or a ceiling diffuser with vanes directed away from the vent register.
• The vent register area must accommodate at least a 10-degree from vertical expansion from the locus of pan bases. The tangent of 10 deg. is 0.176. This value times the distance from cooktop to the ceiling is the overlap required past the cooktop edge all around the cooktop. This may require more than one ceiling unit. Even larger than this may be needed based on whatever the normal room air motion is.
• The plume velocity vs. angle is a distribution function; some plume exists at wide angles. Hence the farther a ventilation system is from a cave like shape, the greater the potential for escape of small amounts of plume. So expect some of the cooking effluent to be removed (or deposited) as a room ventilation process rather than a vent hood process.
• A means of cleaning needs to be determined that will keep safe the cooktop surface as well as any counter top stone not exceptionally well supported.
• I have no plume velocity data applicable to the ceiling distance above a pan, but I would expect some reduction from normal hood separation distance due to increased cooling. If we go with 0.6 m/s, or 120 ft/min, and assume a 50% fill by the ceiling baffles or mesh filter, then I'd aim for 60 ft/min average across the large vent area. This makes the required volumetric flow rate (CFM) equal to the total venting area in square feet times 60 ft/min. The blower rated CFM will need to be 1.5X that flow rate for pressure loss compensation. A real analysis based on pressure losses due to whatever the filtering is may be helpful.
• A flush ceiling unit generally has zero reservoir volume. Large cooking transients may not be fully captured and contained even with these requirements met.
• Blower power control will have to be brought to the island or a nearby wall. An induction motor blower may be the easiest to obtain a controller for. Some ceiling units may be supplied with remote controls simplifying this otherwise awkward wiring necessity.
• As usual, the duct size to the outdoors should be such that the air velocity in the duct is in the 1000 to 2000 ft/min range.
• Successful testing (with MUA functional) requires watching the plume behavior when subjected to smoking peanut oil, not just watching steam rise.

Looking at the picture from Opaone, the big issue is obvious. The hood is not deep enough. It looks like it is a standard depth hood liner, not a pro depth. Two things at play because of that, one is there isn't enough holding capacity in the hood. It can't capture and hold (for the blowers to remove) the contaminates that are being generated. Second is the hood needs to be deep enough to cover at least half of the front burners for it to have any chance at being effective. Likely a designer nixed the idea of a deeper hood because "people don't like them that deep and they'll hit there head". Wrong size hood for the application.

Also, on noise, if a hood is working and doing it's job it's going to make noise. Most of the noise comes from the air changing direction. Some hoods have multispeed blowers that can run low and quiet, but at that speed you're just simmering or sneaking a heater in the kitchen. Even remote blowers are going to generate upwards of 70db when they're sucking air through baffle filters. Best case, the hood is working well and you can at least have a conversation when standing in front of it.

@Michael, you are largely correct on the depth issue which is capture area. What you refer to as 'hold' is called containment, containment area or containment volume. Both capture area and containment volume need to be adequate and I am not aware of any consumer hoods that are adequate for these. And FWIW, 'pro depth' is 36"-42" clear open aperture. I'm not aware of any consumer hood deeper than 29" and none with a clear open aperture of more than 25".

You are incorrect on the noise. It is possible to have extremely quiet hoods that are effective in effluent removal.

Our hood (search on here for 'commercial hood install') at 550 CFM actual measured CFM (equiv to about a '1000 CFM' consumer hood on high) is effectively silent. It cannot be heard above an ambient noise level of 32dB(a). When we were having problems with the programming on the controller we actually had to adjust the low speed to 600 CFM in order to hear if the hood was running or not. And FWIW, I'd guess that our hood on low is more effective with effluent removal than any consumer hood on high.

My thoughts on hood reservoir vs. CFM aspect are as follows:

For most residential hoods with minimal reservoir volume below the baffles, the velocity of air into the hood aperture has to be at least one-half the velocity of the plume so that the baffle gaps will be operating near the velocity of the plume. For hot but otherwise steady-state cooking, this requires around 90 ft/min (see MEDIUM column in figure below from the Greenheck Guide). Containment of transient plumes with greater velocity may be inadequate.

For commercial hoods with large reservoir volumes below the baffles, the velocity of air into the hood aperture has to be sufficient to equal half the area weighted velocity of plumes entering the hood. E.g., if a single plume at entry covers 1/4 of the hood entry aperture, one could get away with a hood entry aperture velocity of one-quarter of 90 ft/min. More would be needed for large plume transients, but generally less than for residential hoods.

Keep in mind, however, that the area of the entry aperture is larger on commercial hoods, so the relative savings in entry air velocity do not correspond to the same savings in CFM.

Also, for cooking not normally representative of residential activity, the air intake velocities listed the Greenheck Guide should be obtained. I believe these apply to cooktops performing the listed task over their entire surface, and hence the plume fills the aperture essentially eliminating any averaging advantage.

It is both far more complicated than that and much simpler than that.

Simpler - The Greenheck info was produced by the Accurex engineers that we worked with on our system. From what they told me the standard basis that they work from is a defined open capture area and an enclosed containment volume (what I believe you call reservoir) that is 18x the capture area. So if you have a 10"x10" (=100 sq inches) open capture area then a containment volume of 1800 cubic inches (100 x 18) results in a 'standard' hood and that is what most of their charts are based on.

So if you have a 'standard hood' AND you are using one of a standard grouping of baffles then you can calculate CFM from a 'standard' chart. Some baffles have a higher minimum requirement or function at a lower CFM and so adjustment factors for these are available.

Two critical notes; 1) Open capture area is less ANY impediments. ANYTHING that intrudes in to the lower 1/4 of the capture area is considered an impediment and reduces the capture area. 2) The 18x is clear open volume. Anything that intrudes in to it, including lights, baffles, fire suppression, etc must be deducted. This is why commercial hoods are almost universally 24" high - so that once baffles, lights and other bits are subtracted out the hood still has a clear open volume of 18x the capture area.

ANYTIME there is variation from a standard hood (E.G., an 18x hood) then the charts and calculations are much different. They do have a number of 'defined hoods' that are not standard hoods but that they have produced special charts and design formulas for since these are used somewhat often. A back shelf hood is one example.

More Complicated - ANYTIME there is a variation from a 'standard hood' or a 'defined hood' then the engineers must do the system design. The worksheets and formulas required for this are quite extensive. As they told me, they do sometimes have to reduce the containment volume below 18x and doing so requires huge increases in exhaust CFM's to maintain extraction performance. E.G., to remove the same effluent as a hood that meets the 18x standard. And this obviously results in very significant increases in noise as well as overall cost (more expensive MUA, more energy used for conditioning MUA, etc.)

So... If that chart you posted didn't say otherwise then it is likely for a standard hood with containment volume of 18x the clear open capture area and a clear open capture area sized appropriate for the appliance under it.

For example. For a Best, Wolf or similar hood with their very limited containment volume to have the same extraction performance as our hood would, IIRC, require something like 13x the CFM's of our hood. HOWEVER, they pointed out that for it to be 90% as effective as our hood would require only about 6x the CFM's of our hood. So the Best hood at 3,000 CFM's would perform about 90% as well as our hood at 500 CFM's. And for 80% of the performance would be 3x the CFM's. This is assuming a 30" depth though (or that all cooking is done on the back burners).

Hope this makes sense.

I'm not sure what the exact EU requirements are on hood noise. I believe that the noise information has to be available for every hood offered for sale but I'm not aware of their yet having maximums allowable.

As they've become more aware of the impact of noise on mental health (which affects physical health) they have been doing a lot more to reduce common sources of the worst noise so I'd guess that if they don't yet have limits, they soon will.

One example. They do have a lot of restrictions on tyre noise (and this is evident when you travel back and forth between the EU and US). Every tyre must be tested and labeled for noise and there are some hefty penalties for higher noise tyres. They also put a lot of effort in to other areas of traffic noise with quieter road surfaces, angled barriers that reflect noise up (there's nothing like picking a Dutch engineer up at a U.S. airport and hearing his commentary on the vertical walls along our motorways), vegetation, and efforts to reduce how much people drive - especially in centers.

Hi There- thanks for sharing this information. We are working on our new build with high ceilings so trying to decide on our hood ventilation now, so that he contractor is aware when building the roof. I see that you don't recommend VAH. Who would you recommend? I have a 36 inch gas range. Thanks!

@Theana Angelus: Please start a new thread with this question. Answers would clutter the FAQ.

The suitability of VaH offerings vary. Also, your question itself may be partially or fully answered by searching for threads using 'hood' and 'MUA' as topics. At the very least, more considerations may become apparent.

@Theana Angelus If you want a simple answer, get any Wolf vent hood, and you will be fine. That is what @kaseki and I both have after researching many factors. Other hoods are also possible, but Wolf is the go-to answer for someone who wants an easy solution that works and works well. Wolf hoods are all of professional style and have the shapes and blowers that you would want to see in an ideal setup. If you have more complicated factors to discuss, please start a new thread.

@Theana Angelus Also remember that for best performance, the vent hood should be a minimum of 6" wider than the range. So, for your 36" wide range, you should be looking at 42" wide vent hoods.

Bump

@opaone, @kaseki,

My architect claims there are newer vent hoods with internal blowers that may be quieter than hoods with remote blowers. I also saw an article recently that indicated there are newer electronic motor controls that reduce the "growling" of fan motors.

Have either of you seen "newer quieter" vent hoods with internal blowers?

I realize there are many factors other than fan noise that contribute to perceived noise at the cooktop, so reducing one source of noise is only helpful if other sources are not increased. I suspect there is no such thing as the generalization offered by my architect.

My last hood was based on a custom insert made by Modern-Aire with a 1400 CFM roof-mounted Abbaka blower. There was no silencer. I thought the hood would be quieter than it actually was. My impression is that most of the noise was from air rushing through the hood baffles, but I don't know for certain.

I used a lot of the information provided by kaseki (about ten years ago) in designing my last hood in terms of capture area and more, and I appreciated the fantastic advice. For the most part there was "no smoke/odor left behind"...

I'm open to your observations on whether there are newer/quieter vent hoods with internal blowers? And no, I am not going with Vent-A-Hood.

Thanks,

BillyG

One can imagine that mulitpole motors driven by synthesized multi-phase waveforms would have less 'hum' than a standard induction motor running from 60 Hz, but YMMV. There might also be a reduction in vibration induced into the roof structure supporting such a blower, or into a hood structure supporting such a blower, but I suspect fan unbalance to be a greater cause of vibration in real life.

With a competent motor design and balanced fan assembly, dominant blower noise at full power should be blade tip (or edge) turbulence noise. Duct turbulence will also contribute. Silencers can significantly reduce these particular noises. Turbulence noise from the baffles can only be affected by the baffle aerodynamic design, as driven by practical and affordable sheet metal designs, so given a silencer baffle noise should dominate, as it does for me.

I try to restrict my commentary to requirements for good cooktop ventilation, and do not investigate hoods for relative noise. I live in a residence, not a test kitchen. It should be obvious that a purported quiet motor design used internally in a hood could also be adapted to an external blower, or to an in-line blower, so in-hood is not a requirement for their application. An internal blower may be the most practical approach for many; but an over-capable commercial up-blast roof blower or in-line axial blower run at low speed will certainly be quieter than when one is pushing high volumetric flow rates from within a reasonable sized hood.

I'll bet even this high internal volume hood uses an external blower.

Handcrafted Metal, Inc.

There are a number of elements that contribute to noise; room static pressure, hood design, baffles, hood to duct xition, duct, blower, wall/roof cap. If you pay attention to all of these you can have a very effective and quiet system.

As well, a proper hood with proper aperture and containment allows lower CFM's for the same effluent removal effectiveness which lessens the noise from all elements.

It is possible to build a blower that itself is quieter than the Accurex that we have but it requires a rather large box and the machining of the parts is quite expensive due to the accuracy involved. My BIL makes these (actually for liquids but works w/ air/gas) and they can move about 4,000 CFM's with almost zero noise. It's amazing what $500k will buy you. :-)

It's probably possible to do something that's 95% as good for 5% of the cost but that's still a lot of money for little gain when a silencer in the path can do 95% of that for 5% of the cost. :-)

I think for effectiveness per dB the best option is a commercial system like we did. I can't think of any other way to get a better ratio or improve on what we have.

It'd be interesting to know if there is something better though.

kaseki, everything you say makes sense to me. That is one amazing vent hood in the photo!! I agree is doesn't use an internal blower...

opaone, thank you for your insights. My kitchen designer doesn't like the size of the hood I dictated to him, but that's too bad. It's almost worthless to have a hood that doesn't function well.

I am intrigued by your Accurex system. Which Accurex blower did you use - an updraft?

Thanks.

I went with a Wolf pyramid style hood with internal blower that maxes out at 350 cfm to meet local building codes that require makeup air systems for blowers over 400 cfm. At max speed it is so quiet you barely notice it on, and I have used it to effectively exhaust some very powerful glue fumes from countertop installation and fissure repair as the kitchen remodel is winding down. I look forward to seeing how well it will do with cooking effluent, and like others, I selected the hood based on the advice of @kaseki and others here at Houzz to maximize capture and containment shape.

@billy_g, blower is a XID-VG inline. Per Accurex recommendation it is a 1400 CFM (free air flow) rated blower that is run at 85% (≈1200 CFM) max. Actual measured performance is 960 CFM IIRC. We run it on low (550 CFM) about 90% of the time.

More: https://www.houzz.com/discussions/5745986/commercial-range-hood-install

opaone, thank you for this information. I appreciate it. Do you recall what fan size and motor size you used to build the 1400CFM XID-VG blower? Did I read correctly that your duct size is 18 inches?

The Accurex website and story is impressive. It looks like I would work with a local representative for design and recommendations, correct?

Thanks!

@kaseki, what is the purpose of the sheet metal bend for the "mechanical baffle" portion of the hood below? Is it to increase the velocity of the air movement at the front of the hood to help trap a rising plume, and/or is it to help keep smoke/grease air in the containment area instead of being reflected out by the baffles? Or maybe it has a different purpose?

Would you recommend having this sheet metal bend or not?

The drawing is from a Captive-Aire web page

https://www.captiveaire.com/CATALOGCONTENT/HOODS/ND2/index.ASP?catid=291

Thanks.

My guess is that it deflects the plume toward the baffles without decreasing the reservoir volume by much.

I see. Thanks.

Today I should receive revised drawings from my KD and I expect I'll make some revisions to the hood design (wood hood with liner) to increase the containment volume. I'll need to figure out whether to go with the sheet metal shop used by the KD versus having something made by a company like Accurex or CaptiveAire.

The front baffle creates a circular motion of air in the hood that helps to keep effluent in the hood until it can be exhausted. It reduces stack effect bounce.

Thanks for the clarification.

Thanks -- it looks like a worthwhile sheet metal bend that helps containment.

Updated FAQ is here: https://bamasotan.us/range-exhaust-hood-faq/

@opaone, Did Accurex have any problems working with you as a residential customer instead of in a commercial setting? Do you have any suggestions as far as contacts or should I go through a local distributor/salesperson?

Were there any modifications you made to their hood design for use as an insert to a wood hood as opposed to a freestanding stainless steel canopy? I probably will ask them to include a flange on the bottom to overlap the bottom edge of the wooden hood.

I really appreciate your discussion of your hood system design which is clearly superior to any other residential system, including the Modernaire system I used in my last kitchen.

Thanks,

BillyG

Yeah, this is at the top of our we're really glad we did that list.

Accurex were quite good to work with as was our local rep. I believe all of their sales are through reps/distributors. Highly recommended.

Their standard front to back depth is 36". They made one for us that's 30" deep but otherwise their standard product.

We discussed the lip and everyone agreed that doing wood the way that we did should be OK given the height. I had a temp logger stuck on it for a while and nothing approaching combustion temps for wood or paint nor max exposure temp for paint. Due to Covid we've not done a very range heavy meal yet though I don't expect any problems.

We are controlling the lights and blowers directly with our Control4 system instead of the Accurex controller which has worked out quite well. It's important to find out from the engineers what the lowest rate is.

@opaone Thanks so much for sharing your experience.

Is the insert itself 30" deep, or does that include the wood hood? Did they keep the 3" airspace in back of the hood or eliminate it because this is residential?

Right now my hood is 28-1/2" from the back wall and the bottom is 70" from the floor. I may need to raise it a bit if it is projecting more. What is the height of the bottom of your hood? I remember reading it somewhere and I seem to recall it was higher than 72".

I may look into the Control4 system because I have a lot going on with lights in the kitchen, which is being added to pre-existing challenging space with a 16' cathedral ceiling.

Thank you.

I see, the bottom of your hood is 6'5" above the floor. Every time I read your FAQ something else jumps out at me. Thank you for writing up your analysis and commentary.

@opaone, I spoke with my local Accurex representative and they told me they cannot make a hood (or insert) that is only 30" deep. They claim that the shallowest they can go is 36". I dug in with more questions and they said that 20" of depth is taken up by the baffles (which are oriented at a 45 degree angle, which is not really relevant) and lighting will not fit in the remaining space. I pushed back again and said lighting should fit in 9 or 10 inches of space and then the rep said it is because of their mass production setup that they cannot make manufacturing adjustments to fabricate a 30 inch deep hood. Bummer. I guess your rep was more willing to work with you.

Billy

Try these guys: https://www.horizonequipment.com

Thanks!

@billy_g, curious if you had any further success in your commercial hood investigations. Based on this thread, I've made some inquiries of my own, and thus far haven't found anyone doing commercial hood sales in my area (Northeast) willing to entertain a residential install, nor anyone willing to wade through the regulatory headaches of an install in a different state (can't really fault them on this one). I've reached out to Accurex, haven't heard back yet.

Definitely a bummer though, I'm really digging the hood @opaone has, for all the reasons listed (and my hat's off to the quality research/analysis, from all contributors, that went into the FAQ!).

If the commercial angle doesn't pan out, I may head down the path of a residential hood liner, and finding a local shop to do a sheet metal extension. Anyone have recommendations for liner vendors/models that would lend themselves to such a modification that might be "almost as good" as the hood @opaone installed?

I see that Abbaka apparently does custom hoods, I think I'll contact them to see whether that offering extends to making essentially a big boxy liner.

You can purchase some of those commercial hoods online and then get local help for installation. The components should be the same as residential hood configurations of various types depending on blower placement and exhaust path; only the size would be scaled up. Look into Wolf hoods before you cross off pro-style hoods. They have depth, capacity, and baffle angle that stands out above most of the competition in the pro-style hood arena. It would be a step below commercial for you but probably meet all your needs in terms of exhaust.

Please move further discussions to: https://www.houzz.com/discussions/6099827/exhaust-hood-faq-ii

@Aglitter did you use the Wolf 400CFM internal blower? or an inline option. Thanks!

I used the Wolf 350 CFM blower positioned in the hood unit itself to meet my local building code since I did not have a makeup air (MUA) system. The hood has been effective for everything including searing steak.