Hi - this thread is a little old now so this might be too late, but I have some related Qs even after reading all this helpful advice. I'm starting gut reno of a 120+ year old townhouse in NYC and plan to install 36" bluestar with 2, 22K BTU burners (in addition to other smaller burners of course) which we'll use primarily for stir fry. We HATE grease smell in the house and cook all the time, so want to get what we need for the stove we have. So I'm fine getting major CFM, if that's what it takes, but my concern is the ducting. It seems we have 2 options - up an existing chimney (which we're having relined and is not used for fireplaces; fireplaces were all sealed up decades ago) - but that would be 3 stories or about 50 feet needed to get to the roof and I wonder if that's too far for it to function properly...2nd option would be to bring it down into a soffit on the floor below (a rental apartment that already has a dropped ceiling) and vent out of the exterior wall, but this would require making a new hole in our masonry, and would mean the venting would be just outside our kitchen, under a french door that we're likely to want to open often while we're cooking - so the smoke could in theory end up back in the kitchen, no? I am by no means an expert so forgive me if I'm totally off base here, but any thoughts/advice would be much appreciated. Thanks!

To make a long story short, I have two Kobe 30" undercabinet hoods. One is the 122 and the other is the 27 with baffle filters. I originaly had 5" duct and adapted the 7" fitting to the 5" pipe. The duct also has some bends because the plumber decided to run the gas line in the ceiling right where the duct wants to be. The air draw really sucked. It was so bad it would not even hold a klennex to the baffles on the low setting which is claimed to pull 280 cfm. Kobe sent me the 122 without baffles as a fix. It was a little better. The baffles themselves reduce air flow. I upgraded the duct to 6". This was the largest size I could get due to the gas pipe blocking the way of anyting larger. It did help a bit but to get any decent draw I need to put the blower on a higher setting, making more noise. My experience with Kobe (the company) was very good. They answered my calls and stood behind thier product. The product is of decent quality. It is designed in Japan and built in China. The 27 had poorly made baffles, they are stamped in two parts and riveted together. The ones I had were warped and one rivet was not installed properly and would not fit. Kobe sent me a new set promptly. I used a Radio Shack sound pressure meter to measure the noise. With the 27, without baffles installed the hood is essentially silent on the low setting. It didn't move any air, but it was silent. The meter goes down to 50db and it did not register with the meter sitting on the cooktop. With the baffles installed it was about 65db. Not exactly silent. The air moving through the baffles is the cause. On high is is fairly loud. The 122 has no baffles and is more quiet and moves better air. The right side of the 122 hood was not welded properly and is not flat. I didn't ask Kobe to replace it though sicne they shipped that one to me to correct the issue with the 27. Uninstalled the hoods move a lot of air. I could blow a column of air across the room. Proper ducting is important. The Kobe hood was one of the few seamless hoods that fit under my cabinets at the right height. It has a nice seamless look, the controls are a little odd but you get used to them. It is not as quiet as they claim. I like the looks of the 27 hood but I have the 122 installed. I may consider a fantech inline fan to pull more air. In that case I may reinstall the 27. Hope that helps.

I needed more than 600 cfm, and the next size they offered was 1200 cfm (two 600's working together). That's internal blowers venting straight out the back, so there isn't really a drop off in amount of air moved like one would get for extended ductwork. There's a continuous speed control knob. I don't know what the lowest volume is, but I'd guess, comparing my previous hood, that it's in the range of 450-650 cfm. If I'm just stirring up a simple sauce, sauteing an onion or boiling up steamy stuff, I run my hood pretty low. Partially that's for the noise, but really it's all that's needed. If there isn't any steam or smell going around the house, that's all I care about. For frying, boiling down stock, or cookingpalooza for the whole gang, I run it at medium high to high. Medium high is usually enough unless I have all burners going. If there's a correlation to how far I turn the knob it's probably around 900-1000 cfm. I don't have a make-up air system. The experts didn't think it was necessary given the particulars of my house. There's little opportunity for backdrafting, though I have sometimes wondered about the pressure thing. When I have run it at full power, I have sometimes felt that the oxygen was being sucked out, but that might well be part neurosis and part from having dozens of people inside with the doors and windows shut and damp out (which is why the shut doors and windows). At that point, the gas burners and the ovens are heating the kitchen anyway, so I'll just open the little casements in my garden window (like wing windows on an old sedan). There isn't a lot of in-sucking at the windows, however, so I think it's more the people breathing the air rather than a real problem with vacuum/pressure. The house is insulated but not air tight. Hope this helps.

We have the KA combo convection oven and the cooling fan is quite noticeable. It's also on whenever the convection is on, so I'm not sure if it's the convection fan or the cooling fan, but I suspect it's the cooling fan. We have a pretty loud house (dog, boys, parrots, music, news, etc) and open floor plan, so it doesn't really bother us. I do appreciate it because it works really, really well to dissipate the heat. Living in Florida and trying to conserve a/c, I don't want a "hot spot" in my kitchen, especially right in the middle of my galley-shape. For this reason I also really, really like my ventilation hood and I use it even when I'm using the oven on my range.