The general approach is to have a hood fabricated such that it has all the necessary internal baffles, lights, whatever in the size and decor you want. Such an approach can reduce the overall amount of sheet metal needed.

Here are examples of refined exteriors: http://www.handcraftedmetal.com/ where I expect the interiors are built in.

For a more commercial look any of the commercial suppliers, such as CaptiveAire can meet requirements.

In your case, I would evaluate the possibility of having an external shell fabricated that tapers such that somewhere higher in the hood it will fit an existing insert.

Patrick...thank you! That is exactly what I needed to hear. Anything larger than a 66" insert is a custom order and requires a longer turn around time. So perfect! kaseki...thank you as well! We are actually looking for a wood cabinet to enclose the insert rather than a metal or commercial look but thank you for responding. All advice is highly appreciated.

@THE FRENCH BARN - Lacanche Canada Hope I'm not hijacking this thread but I have exactly the same quandary. We have a Citeaux with the 2 induction burners at the end just like @tcvino . So the range top is 59" x 25 1/2" and we were planning on a hood that was 66x28? It's an island hood too which makes the selection of inserts much smaller. Can we make an insert that is 58 3/8" x 22 1/2" work for us? Should it be flushly mounted on the bottom of the hood, or recessed a bit? I've never seen them not flush-mounted and that would also affect the height from the cooktop surface meaning I'd have to lower the hood even more which I hate to do...arggggh this is so frustrating!

@snafu , I wont pretend to be a ventilation expert with the ideal answer for all situations, so a 66" x 28" hood with a 58" insert should work for your Citeaux. In an island setting, the extra width / depth is even more important.

Most inserts are indeed somewhat recessed into the hood. This helps to capture the fumes / smoke before they get sucked in by the blower.

While the technical considerations are certainly important, your setup should also be usable on a daily basis. If the hood is too low and makes cooking uncomfortable, it doesn't really matter how well it works, and vice-versa: you may have a beautiful hood that completely blends into your design, but if it doesn't suck anything out, it's not that great either! It's a matter of finding the right balance for your space, cooking style, and technical requirements and restrictions.

Welcome to the Lacanche family!

Patrick

I think, snafu mcsnurf, that the question to be answered first is whether the outer shell (surround) that is to receive the insert is combustible (e.g., wood cabinet continuation) or non-combustible (some metal structure). In the latter case, the outer shell can act as part of the overall hood function by capturing and funneling the plume to the insert containing the baffles. In the former case, the wood must be covered on the interior and I would argue for covering the bottom edge even if beyond the combustible distance limit specified by the stove fabricator. I imagine that a sheet metal shop could build an insert extension for a wood surround that would mate with a 'standard' insert. Lighting may be a problem is one has to reach too far up into the hood.

However, all this sizing really needs to start with some fundamentals, so let me go over them again. For more detail, read the hood threads in this forum back to 2008.

Capture area must overlap the cooking surfaces (pan bases, griddle surfaces, grill surfaces, etc.) by enough given the hood entry aperture mounting height that effluent cones from those surfaces expanding at 10-degrees from vertical are intercepted. This is a more fundamental rule than rules based on overlaps defined by the cooktop or stove boundary dimensions. For island hoods, even more may be needed if there are cross currents (drafts) moving the rising and expanding plumes.

Containment air velocity at the entry aperture performing the capture should be aimed at around 90 ft/min, which is equivalent to 90 CFM/sq. ft. of hood entry aperture. (Conversion to metric is left as an exercise for the student.)

Note: While it is true that induction cooking lacks the combustion plume of gas cooking, and hence has a lower peak effluent velocity at modest cooking levels, all-out searing or wokking will bring the plume velocities close enough that skimping on the containment velocity using induction as an argument will likely degrade containment. The 10-degree number is just a point on the plume shape so gaining a tiny bit of effective capture area expansion due to inflowing air at the hood edges is helpful.

Second note: Moving inserts up into a hood surround is a somewhat desperate act, and I would recommend a custom insert as a better approach. Please realize that in the larger hood sizes, the production rate is less than for the 30- and 36-inch sizes, hence fully automated cut and weld tooling is less likely to be used. Thus the amount of labor needed for a custom size should not be a lot more than for some fabricator's standard size, given similar standards of fit and finish.

Blower scaling should account for the blower's fan curve and all the system pressure losses going from the stove top to outside and back to the stove top, so make-up air pressure loss has to be planned for and evaluated, along with baffle loss and duct loss. Lacking such an analysis, I suggest that a multiplying factor of 1.5 be applied to the calculated required flow rate to determine the blower's rated (zero pressure loss) flow rate to account for the fan curve and the various pressure loss 'sins' that are likely, but this assumes that the MUA is not too lossy. (In any case, lossy MUA drives house relative pressure negative, which is a safety hazard in many residential situations.)

Noise control is another aspect treated in many threads here.

MUA insertion into the kitchen to avoid drafts must be performed with care.

kas

@kaseki We discussed most of this already in a couple other threads. I've also read your excellent FAQ you put together with opaone . You probably find yourself answering the same questions repeatedly on these forums so it's become a blur, but here is the thread you were helping me with: [https://www.houzz.com/discussions/range-hood-liners-inserts-blowers-oh-my-dsvw-vd~5229208 [(https://www.houzz.com/discussions/range-hood-liners-inserts-blowers-oh-my-dsvw-vd~5229208)

To refresh a bit, it's an all metal island hood with an external blower

So I think I have a pretty good handle on how to build a system that is effective, efficient and relatively quiet. The thrust of the final thing I'm trying to decide is how much smaller than the hood enclosure is 'acceptable' for an insert to be effective? Certainly the larger capture area helps, but does that effect get offset by having a smaller insert in there? I mentioned the BEST insert is 58 3/8" x 22 1/2", I spoke with Modernaire as well and they have one the same width but 25 1/2 deep but it's $1000 more and the remote blower is slightly less powerful (1400 cfm vs 1500 cfm). I could get a custom built Modernaire too, but again that's an extra $1000 on top of the extra $1000...this gets really expensive really quickly for a piece of metal and some baffles. I'm trying to balance all these factors and make the best overall decision for my kitchen and range. As the saying goes 'perfect is the enemy of good' so at some point you need to compromise somewhere.

... and better is the enemy of good enough.

OK, metal inside metal. What you need then are panels that bring the inside edge of the outer envelope (visible hood) to the outside edge of the inner insert. If these panels have some slope to reflect the plumes inward and upward, then the outer entrance aperture will be the effective hood size.

The insert should be fully effective if you can achieve around 90 CFM/sq. ft. calculated against the outer hood's inside aperture with such panels.

Another way to look at it is to consider a typical commercial cooking appliance hood. The hood is wide and long, but the baffles are not covering that entry space. Instead they are internally farther up, typically are only one row, maybe with sloping hood interior sides to bring the effluent to them and sometimes not even that. The opportunity for effluent to reflect out instead of being contained behind the baffles is significant. This is why they need air flow rates scaled by their entry aperture and not the baffle area, because otherwise, smoke can reflect out of the hood before getting to the baffles.

An example of one configuration like this is illustrated by a sketch taken from the Greenheck guide.

And I would note from experience here that nearly all of us have anticipated having a kitchen renovation without fully appreciating how much adequate ventilation (incoming and outgoing) will cost, even without the exposed parts meeting some desired level of aesthetics.

kas

OK I'm sorry, but now you're starting to talk in circles and contradict yourself.

In one breath you say:

"OK, metal inside metal. What you need then are panels that bring the inside edge of the outer envelope (visible hood) to the outside edge of the inner insert. If these panels have some slope to reflect the plumes inward and upward, then the outer entrance aperture will be the effective hood size."

after you literally just said:

"Second note: Moving inserts up into a hood surround is a somewhat desperate act, and I would recommend a custom insert as a better approach"

The insert either has to be flush mounted, in which case there is no angle/slope involved, or it has to be recessed into the hood so as to achieve the slope you recommend. You can't have it both ways.

And what exactly are you basing these statements on? I'm not disagreeing that the idea of a sloped piece of metal 'should' help maintain the scoop like shape of the hood and perhaps funnel smoke into the insert to be collected, but you're also moving the insert further away from the source by doing this and we all know how important hood height off cooking surface is.

I had the impression that you are building an outer cabinet of metal that performs the function of a hood exterior. This could have any shape until you declare just how the insert is intended to fit into it. In the general case, the insert could for many external shapes not fill the interior of the shapes. In such as case, the sloped metal pieces would connect the two without leaving any grease catching gaps.

Hood height off of the cooking surface, for a nested insert, is determined by the exterior structure lower edges and not necessarily the insert's lower edges, unless the insert is below flush with the bottom. Your earlier messages indicated that there was going to be a gap between the outer structure and the insert. I have been trying to describe various ways of dealing with that condition.

I think that the images I have constructed from your words are different from what you intend and that the images you are constructing from my words are different from what I intend. In my images, there is no contradiction -- only an opinion of the relative optimality of different configurations.

It may help for you to provide a sectional drawing (sketch) of the outer structure with a candidate insert shown within it so I can get my image aligned with yours.

"Hood height off of the cooking surface, for a nested insert, is determined by the exterior structure lower edges and not necessarily the insert's lower edges, unless the insert is below flush with the bottom. Your earlier messages indicated that there was going to be a gap between the outer structure and the insert. I have been trying to describe various ways of dealing with that condition."

I'm not sure where you would get that impression, I never suggested that I would leave a gap between the insert and the surrounding hood, I can't even wrap my head around how they would construct such a hood? What would the insert attach to if there was no metal between the two? While they do make inserts in numerous sizes.... for large island style hoods (larger than 48" wide) the options become extremely limited. So the point of the question is "all other things being equal, at what point is a given insert TOO SMALL to effectively service the surrounding hood enclosure". Clearly a little 32x14 insert is not going to work very well because it's only half as wide and deep as my enclosure and makes up only about 1/4 of the total sq ft underneath the hood would you not agree? But what's the cut off point? How much smaller than the enclosure is acceptable to get the performance you want? Or perhaps a better way to put it might be to start with the position that an insert that 100% fills the enclosure is the baseline best option, it gets 100/100 pts. How does that graph look as the size of the insert decreases?

Here are some diagrams to illustrate what I'm talking about. There are all to scale. The blue rectangle represents the hood enclosure, the insert is within them (note: I used the BEST model insert image for both because Modernaire's website is crap and they have no images of the unit head on)

The extra depth probably helps a bit but I think an extra half foot of length would be more beneficial because the actual intake area would be expanded much more.

I suspect that I mixed up the initial requirements that would apply to the OP, tcvino, and those that would apply to you, mcsnerf.

Large metal island hoods, such as my Wolf, do not normally have inserts. The baffle assemblies mount to the hood structure and the lights are embedded in the hood structure. See image. There is some interior sheet metal not part of the outer skin above the baffle assemblies, but these pieces are not structural and mainly serve to protect electronics.

In my experience, inserts are used with non-metallic enclosures, such as wood, stone, brick, or sheetrock to hide the ventilation. I think that the understanding I missed in our earlier conversation is that the blue represents lower edge horizontal sheet metal on which your insert sits. It essentially connects the insert to the enclosure. Is this correct? Otherwise, one might believe that the outer edge of the blue is the outer edge of the enclosure, and that the enclosure, being thin sheet metal, leaves a gap represented by the blue. The insert in such a case would be structurally supported at its top.

Assuming that the insert sits on the blue flat surface, then we get into the not easily evaluated case where part of each plume is striking a blue area, and can partially reflect away from the insert, biased by whatever intake air breeze is moving across that space. Capture and containment may require a very high flow rate to ensure that all around the island hood the transverse air flow at the lip is commensurate with the meter per second rising plume. This would be very noisy, and require considerable MUA. This is why the goal is to have the entrance aperture overlap the plumes, and your entrance aperture is only the open portion of the insert.

The blue area doesn't count as overlap (perhaps partial overlap) unless you put the blue support higher in the enclosure and thus support the insert higher up. In that case the plumes will enter the enclosure capture volume and reflections at the [blue] insert base support will have a better chance of being contained. Just guessing here, but this might require raising the insert ten to twelve inches for full effectiveness.

Before commenting further, please let me know if I am now clear about your intent.

kas

Hello! That's exactly what we are going with. I don't have pics yet as it was just ordered. Will try and remember to send as soon as I have something!