Berbel extractor hood has the best recirculating technology but currently only available in Germany and UK. In conventional hoods grease is absorbed in filters. Grease particles clog the pores of the filter, and hood performance is reduced in increasing proportions. With the berbel principle grease is accelerated out of the air by centrifugal force, and is effectively separated at two points. The interior of the fan box remains virtually free of grease particles. There are no consequential costs, no unpleasant odors, no vermin, and there is no fire hazard. With berbel the unit can be cleaned with just one wipe, as easy as cleaning a Ceran hob. The stainless steel tray is made of the highest quality stainless steel and thus is dishwasher safe. http://www.berbel.de/int/index.php?id=300351 http://www.berbel.de/int/index.php?id=10

houses14, my Imperial range hood is not an insert, rather an under cabinet ss hood. However, the materials used, and the quality of construction, the fan motors, are the same with minor variances to allow for space restrictions within the smaller size of my hood. Construction wise, it is all that I had hoped for, was easy to install, and has functioned beautifully. Packaging and shipping were excellent. The ss is marine grade. This means that the amount of chromium in the ss will prevent rust from forming in the interior of the hood over time. The electrician informed me that their fan motors and switches appeared to be top quality. The warranty for my hood is 7 years, which is almost unheard of in the industry. Their specifications and installation instructions are right on to allow for optimal operation. For example, my duct is 8" from hood to roof jack and had to have a certain rise in height from the hood before the first angle in the duct work. Baffles remove and reinstall easily for cleaning. It was a joy to call Imperial direct with technical questions at their manufacturing headquarters in California. Someone was always immediately available to answer my questions regarding their vent hoods or recommended installation. My installer was promptly referred to their engineer for technical assistance as I requested that the wiring that would automatically turn on my hood once a certain temperature below the hood was reached be disconnected as I did not want that feature. To me, having that level of service available when answers are needed means a great deal. I found that the folks at headquarters were always honest even if it wasn't the answer I wanted and that they knew their stuff. Their light and fan switches are continuously variable which is rare on vent hoods. This means that they both function like a rheostat with a continuous increase, or decrease, rather than clicking up or down discreet notches, such as level 1 to 4. Also, I liked having the option of installing the switches wherever I wanted remotely, rather than being mounted to the underside of the hood. The hood easily handles removal of odors, steam or grease beneath it's surface. I've found that if the hood is allowed to run for about 10 minutes prior to cooking that it can be operated at a lower level and do a good job. The hood on low is fairly quiet but is noisier than I had anticipated at higher levels with having dual fans and baffles. Also, highest cfm level is 1000 which is a factor. However, I used a different size led bulb than Imperial recommended. I now have a gap around the bulb that needs to be filled with a rubber gasket. Also, the temporary roof jack is too large, and the correct one is waiting to be installed so the jury is still out on the noise issue. Noise level was quite an issue for me, but even if it remains unchanged, I would still buy the same hood given how pleased I am with the overall operation and that I can easily live with the noise that I now have. I'll have to look up the name of the online vendor I used and will add that information tonight.

I don't understand why the question for Makeup Air is being asked - the house has an HRV system with ducting elsewhere. This is solely for the range hood exhaust, because I'd likely to avoid those silly Sophie, are you in Canada or the USA, the clearances may be a bit different. (I ask because I've had multiple kitchen designers look at it, I recall checking it myself against code previously, and it wasn't a problem). From a quick google search, it appears I require 30" of vertical clearance, and as drawn I have more than that. Sophie, I'll go home and measure my stock pots. They are a few different sizes, but not huge. (I make 3 pots of soup at once, but in one of the smallest size stock pots they make). For a 33" cabinet it looks like at best ill have ~12.75" of clearance with the door open. I could probably shrink the adjacent cabs if necessary to get to 36", but I'm waiting to see how square the walls go up before I commit.

@3onthetree is correct, within the assumptions presented. However, so long as you are satisfied with well under 200 CFM, you can transition to 4-inch duct. (With the specified 6-inch duct, the blower would probably only push 300 CFM at best, and this assumes very low pressure loss in whatever method you have of providing make-up air. There will be slightly less overall duct pressure loss if the duct to the ceiling is 6 inches rather than 4 inches, but this difference may be trivial depending on how long the 4-inch duct is to the outside. Impingement grease buildup from too high an air velocity may be compensated by not likely actually achieving a very high velocity. Note that even 200 CFM in a 4-inch duct results in a duct velocity of 2300 ft/min, undesirably high, and quite possibly beyond the capability of the hood blower. Ventilating to the outside will usually beat recirculating, but we don't know enough facts to be sure in this case.