To be brief, because this has been covered in various ways in myriad other messages: Fans have a relationship between flow rate (cfm) and the pressure difference across the fan. The rated flow rate of a fan at zero static pressure is measured in open air with, as one might guess, the same pressure on both sides. As the flow is restricted by one means or another, (e.g., the hood aperture transition, baffle losses or mesh losses, duct friction, etc.) the flow rate goes down. Some suppliers will rate their fan hood assemblies, accounting for some of the losses. In this manner they can claim that a 600 cfm assembly equals a 900 cfm fan, but that assumes that the fans have the same fan curve (flow rate vs. pressure drop). Fans are all different, so the only way to really guess what will happen is obtain the fan curve, estimate the losses through the entire system, including the pressure loss from imperfect make-up air, and then see what flow rate is achieved. kas

Check with your local planning department. With 10" ducting, you definitely need a roof jack that doesn't constrict air flow. The standard Vent-A-Hood recommended roof jack is fairly low profile. It seems unlikely that it wouldn't comply with your local wind resistance standards. Are you sure it's not just your roofer's resistance to using something different from what he usually installs? It's a pretty sure bet that yours isn't the only house in Miami-Dade County with a 900 cfm Vent-A-Hood.

I spent some time looking at your other post before running off to make a pie for the family. I do wonder what your duct set up is: do you presently have in line motors or do you vent to outside? Did you go with the Kitchen Aid Range? Do you know what your BTU's are on your choice, and where the largest diameter burners are? Usually at least one is in the front. As to the Imperial vs the Kobe, they both seem as they will offer what you need: a method of venting fumes with a good amount of cfms (720 vs 800) at a height of 30" (presumed). Kobe has the advantage of the motors and draw being right there (no long duct runs) as well as being serviceable right in your kitchen if need be as well as cleaned. And of course the increased depth for effluent capture. AJ Madison says Kobe is known as a "quiet" blower, used in Japan. It also has two motors, with variable draw increasing sound and pull. The Imperial also is impressive, yet even with looking at specs, I couldn't positively tell it was an exterior venter (squirrel cage). Do you know your needed duct circumference? Is it 7 or 8" round? The Slimline ducts only vertically, not through the rear. There is no adaptor so you must know vertical ducting is present. Imperial notes: "*Caution on Ducting: Transitioning a TW (twin duct unit) to a single duct will cut CFM output in half and will void the stated performance and warranty! There are many aspects, including warranty of the Imperial that I like. However, if your duct run is long that 800 cfm's will be reduced, perhaps significantly. Hence, if your new range is a power horse with BTU's, I believe I'd to with increase capture (21," aided btw, by your lateral cabinets as they reduce open space over which effluent travels), and inline motor fan at proper height. Your cabinet constraints are a situation where an extra 3" cabinet set back laterally (for less combustible fire hazard) is not negotiable. Looks good: both are nice choices. I'm glad you're closing in on the decision and hope this helps.

As thr former owner (and slow learner) of two Vent-a-hood installations in two previous homes I can say from experience I found them to be very noisy at all three speeds. Thoroughly cleaning grease deposits was a difficult if not impossible chore. In our present home we recently installed a 36RNB Bluestar range with a Best #WP29M427SB hood and a 1,266 CFM Fantech FKD 10XL in line blower. Results - PERFECT ! No smoke or cooking odors, quiet operation at all speeds and the dishwasher does the cleaning.We couldn't be happier with the results.