An insert is no different than a chimney, it is just hidden under a cabinet clad. Hoods are based on cook size, type, the venting distance, THE SIZE of the kitchen........and make up air. Your model requires a separate kit to be purchased. Specs for mounting should be followed.

you need 100 CFM for every 12" of stove width.
For example a 30" stove (2.5') x 100 CFM= Approx. 250 CFM needed, as a minimum.

A range hood should exchange the air in the kitchen 15 x per hour.

To find the size of fan needed, multiply the cubic feet x the # of air exchanges (15) then divide by 60 (minutes in an hour).

Most gas burners put out approx. 10,000 BTUs per burner. Multiply that by the number of burners, Then divide by 100 to find the minimum CFMs needed. .

Most HVAC suppliers recommend smooth 8" metal pipe. Add 1 CFM per foot of pipe and add 25 CFM for each bend

When all that is considered, Download/ check the specs for your selection and review with your contractor.

CFM are decided by the BTUS of the burnersand in myexperience has nothing to do with the size of the stove,other than it has to be at least as wide as the stove. so your stove instructions will have a suggested rating. A lot depends on how far the venting needs to go before hitting the exterior so that will also have to factored in. As far as the look that is mor eof a personal choice I do not like hoods installed inside cabinetry unless it is a very large traditional kitchen with all the appliances having cabinet fronts. I read that article and find it ia bit over the top for explaining venting. I have a 36” all gas range my vent-a-hood is also 36” wide but with high CFM since often all my burners are used( Ihave a catering biz) my hood vents straight up through a very shallow attic .I have had vent-a-hood s in my last 2 homes and find that bran very reliable and quite nice looking.

Most gas burners put out approx. 10,000 BTUs per burner. Multiply that by the number of burners, Then divide by 100 to find the minimum CFMs needed. .Repeat..That is the MINIMUM and must be considered with venting length and any turns in that venting

Arrrghhh! Effective, efficient, efficacious, etc. -- all desirable qualities that are pretty vague in most people's minds. Let's start with the basics. The primary functions of a hood over a cooking surface are named capture and containment. Both are required.

Capture refers to intercepting the rising and expanding cooking plumes before they escape into the room and potentially coat everything with grease and moisture. Containment refers to getting the captured effluent out of the house.

Capture requires a hood entry aperture that extends beyond the sectional area of all possible cooking plumes that are likely to be generated by the pots and pans (and griddles and grills, where applicable) on the cooktop, measured at the point where the hood entry aperture intercepts the plumes. This is because it is impractical (and generally intolerable) to have a flow rate sufficient to pull effluent into the hood from distances much greater than a fraction of the hood's minimum dimension, and very difficult to do that outside the immediate edge of the aperture. (See Figures 5 and 6 of Chapter 30 of the 2003 ASHRAE Handbook: HVAC Applications.) Hence, capture requires hood overlap of the cooking surface area. The amount of overlap is thus also determined by the height above the cooking surface where the hood entry aperture is placed.

Containment deals with the plume's upward momentum causing it to naturally bounce or reflect out of the hood aperture volume if not (more or less) immediately pulled into the baffles (or other filter) and expelled via the duct path. This requires a sufficient flow rate. For a good treatment of this, see the Greenheck Guide at:

http://www.greenheck.com/media/pdf/otherinfo/KVSApplDesign_catalog.pdf

For typical residential cooking, I recommend 90 CFM/sq. ft. of hood entry aperture to deal with the effluent momentum. This value equals the hood air velocity at that point, which would then be about half the upward velocity that the pans can achieve when very hot. It seems to work and is consistent with Greenheck's recommendation of 85 ft/min for certain cooking activities.

The hood air flow rate needed for effective containment is not the blower flow rate that is attached to the spec sheet. That flow rate is only achieved with the blower hanging in free air (zero static pressure) and not in a ventilation system. Instead the rated flow rate has to be considerably higher to deal with flow restrictions (pressure losses) in the entire ventilation path. Note that this path not only includes the baffles or other filters, hood transitions, duct friction, momentum changes at bends, but also the losses in replacing the air in the house (the make-up air). Without a serious analysis that requires that the rarely available hood pressure losses be known as a function of flow rate, a wild guess is needed for the ratio of blower rated flow rate to required flow rate. I suggest a factor of 1.5.

Other considerations include a duct diameter that allows the required flow rate to have a velocity in the duct (at full power) around 1000 feet per minute minimum, but not over 2000 feet per minute.

With respect to hood shapes, one should appreciate that commercial hoods are made as they are because they are the most efficient at capturing and containing vs. the electrical power used. These may not meet many residential kitchen owners' views of adequate aesthetic design. Nonetheless, choosing designs that are similar to commercial designs is desirable. This means similar aperture area, having some aperture volume before the filter sections, baffle filters for any serious flow rate, and an internal design that brings the flow from outside to the duct with minimal directional changes (except in the baffles where that is their purpose).

Also, consideration should be made to the triumvirate of options: Once cannot have all three of great aesthetics, low cost, and recommended performance at the same time. Either trades among these have to be made, or one sacrificed for the other two.

What type of cooking do you do? Lots of grease? Lots of onions and garlic? Lots of deep frying?

I've had downdrafts, custom hood with insert, regular over the stove microwave with direct vent to outdoors (outside wall) over a 30" gas stove.

The Micro over stove directly vented to outdoors worked great (micro over stove not my favorite). The downdraft JennAir with grill and downdraft worked great. The custom hood with insert was my favorite aesthetically, and vented through the roof and worked fine.

I don't fry a lot of foods (less as time goes on), virtually never deep fry, and use lids a lot because I don't think anything keeps the smell of frying onions contained (just my opinion). Downdrafts seems to get a lot of pushback but the one I had was terrific.

I think you can have reasonable aesthetics, reasonable cost, and reasonable effectiveness :) though perhaps not great :) But though we cook a lot (if guessing, I'd say more than 85% of the population) and microwave very little, I have never felt the need for super-high power and I don't like lingering odors.

If I were doing a new kitchen, I'd do a downdraft because I really lean towards clean lines and more modern interiors.

So, the bottom line I think is to consider how you cook, and if you cook lots and lots of greasy and odiferous foods on a daily basis, super high power performance might outweigh anything else.

Is this new construction or are you remodeling? As Jan mentioned - pipe size matters! Most builders in our area install a 6" pipe for the basic vent insert - which will only handle a minimum cfm. Check to see if you are able to go with a larger pipe before purchasing a new unit. In remodeling, we sometimes find the pipe so trapped it would require a major project to increase the size. Placing a 1200 cfm vent blower on a 6" pipe will result in air being forced backwards out of your vent, along with a lot of noise!

Your model HAS the specs. You have a formula above. You know your range. You know the size of your kitchen.You know the look you want. You know how you cook, how often and WHAT. All fans must be turned on...before cooking begins.

Under the cabinet is to be forgotten at this point.

Kaseki - is that true for inserts that have side skirts/cabinets? When you write about the wide lip, you mean horizontal surrounding the actual metal hood, right?

Thank you for all your expertise.

Features that help constrain the rising plume (imagine for the moment that the blower is off) to enter the hood capture volume instead of missing that volume can make up for a smaller hood aperture overhang. This is why a wall hood can be a bit smaller front to back than an island hood, and why side skirts can allow a hood to be a bit smaller side to side. Cabinets (12 to 15 inches deep) are only partial side skirts, but still help channel the air flow such that it entrains some of the plume thereby helping direct it.

The image one should not have in mind is that the hood sucks up cooking effluent from the pans. Instead one should imagine that the hood waits for the rising effluent to come to it. Left to itself, the plume will diverge (expand) as it rises. The entire plume, however, is susceptible to side drafts, and if the largest side draft is the hood air flow passing by the cook and into a semi fireplace shaped cavity, then the hood overhang can be smaller. In such a configuration the wider lip (thickness of the hood sides at the bottom -- often containing lighting and blower controls in the front) can help direct the effluent that would otherwise strike it and reflect down and out. I would not assume that this effect is significant in plume control with my island hood, but believe it can be a contributor with wall hoods.

"The image one should not have in mind is that the hood sucks up cooking effluent from the pans. Instead one should imagine that the hood waits for the rising effluent to come to it."

Very well said. Hot greasy effluent will rise and spread out as it does so. It takes an enormous amount of effort (air flow) to change its course and the hotter and denser the more difficult it is to change. A hood can only exhaust what rises in to it (and stays contained in it until exhausted). All the rest will spread out in the room.