When the effluent rises it has some velocity, and hence momentum. When it enters the hood it has a tendency to "reflect" and curl downward and potentially escape. If the hood is deep enough (top to bottom) and the hood fan flow is high enough (cfm) the curling effluent will remain captured and will be exhausted. The barrel design in the picture looks to me (without examining one) like it has adequate depth. W.r.t. ya think's question a few messages up: First I would say that the change from vertical to horizontal should be as large a radius curve as you can fit to minimize pressure loss (as well as noise). The effluent momentum (which is a vector) is being changed in direction. This is akin to stopping it and starting it up again. If it can slide along a curve, the momentum loss is significantly less. There is one commercial ducting source I came across once that uses 90-degree transitions, but embeds a curved shape within the duct to improve the flow. I find it hard to answer the question of what questions to ask. Usually, the answers aren't available. Ideally, one would want to know the fan curve (flow vs. static pressure) and try to estimate all the pressure losses (including the pressure one might pull the house down to with or without make-up air) to see what the real maximum flow rate will be. This can then be compared against estimates of effluent generation rate calculated from the reference below. The power used might be adjusted to represent your cooking style, as rarely would one have all burners on maximum and cooking at the highest pan temperature. One thing is certain, flow rate in the hood has to at least equal the flow rate from all the active burners and pans, and arguably should be higher due to imperfect effluent collection. Implied above is that the hood manufacturer can supply pressure loss of the filters vs. flow rate, as well as that of the hood transitions. Getting that data, even if it were ever measured, would be unlikely, me thinks. I suggest that various hoods be "audited" in showrooms to gain a feel for their noisiness versus their designs. The reference worth reading, even if one doesn't intend to use it for calculations, is "Thermal plumes of kitchen appliances: part 2 cooking mode," by Risto, Hannu, and Pekka. (I've found it on-line whenever I've looked for it. Part 1 is also interesting.) If you do use it for calculations, please note the following apparent errors in their Equation 1: The constant should be 0.05 not 5. The units of phi should be kW, not W. (these corrections make their tables consistent with the equation) You will need a scientific calculator or counterpart software to do the exponents (unless you are very old school and know how to do logarithms). You will also need to convert BTU to kW and cubic meters per second to cubic feet per minute. This is left as an exercise for the student. [insert sociopathic laugh here] kas

Despite being a fan (sorry again...) of remote blowers, I still don't think I'd chuck it all for one unless you are truly kitchen and noise obsessed. As I said on the other thread, 95% of blowers have got to be internal (no reference for that, just an educated guess) and most folks are fine with them. No question at max airflow, the internal will be somewhat louder, but again remember that most of the time you won't be doing that. I'm pretty noise sensitive and our lake house VAH hood with 600 cfm blower internally is loud enough to annoy me. Thus when I started with a clean sheet of paper at the main house i went with the whole remote inline blower/silencer setup (which has cost me some time, money, and stress as we've hit the usual problems as we install ductwork). I think it's optimal but not essential (like so much else in this kitchen).

just a followup, i went ahead and ordered the inline fantech fkd10xl along with silencer. also, if anyone is interested in continuous fan control, fantech tech support told me that they also offer a wall switch to do so, called the SCD7. the abakka was also a good choice, but the fantech with silencer was half the price and gave me 66cfm more (not sure it will make much difference in actual performance, but on paper it sounded good to me). abakka customer support was also excellent when i talked with them.. with great reviews for both products, i felt i could not go wrong with either, so i elected to save some money for a faucet upgrade and go with the fantech... thanks everybody for all of your helpful suggestions!!

The Wolf 1500 nominal CFM blower that I have is sourced from Broan as Joe noted above. As I recall, being an induction motor, it requires two-conductor-plus-ground cable, probably with AWG 14 conductors. (If you are desperate to know this, I can get into my attic to look.) Romex (NM) cable should do unless your municipality has some peculiar requirement otherwise. Even an amateur electrician should have the needed cable on hand. My Wolf hood (made by Independent in those days) uses a rheostat-controlled diac/triac circuit for motor control. (This is probably described somewhere on Wikipedia, as well as in various 1970-ish transistor circuit guides, such as the one by GE.) More sophisticated integrated circuit motor controls exist if one wants to initiate a research hobby to look them up. Note: Semiconductor motor controls operate in a reverse direction from lighting controls. Upon turn-on, the motor is given full power to start up, and then further clockwise rotation of the control reduces motor power. (In the diac/triac circuit, the reduction in power is due to increasing amounts of the electrical cycle being removed from the motor power waveform.) The Wolf blower housing has its own damper that opens when the motor starts. I believe it to be forced open by the air pressure. The hood damper is still useful as one wants to keep wind impinging on the system from leaking into the house, and warm household air from leaking past the hood into attic spaces. If your hood doesn't have a damper, order one from Fantech for your size ducting, along with a couple of duct clamps. I'm not sure that locality of repair is really an important factor in a roof-mounted blower. You or your designated victim will have to get up there and remove parts to get the motor out, and then replace it. If a meteor hits the blower, just plan on replacing the entire assembly. While my unit generally keeps the roof below it clear of snow, or at least self clears the snow, in very cold weather with a humidified house damper freezing is possible. If you have very deep snow, a more commercial style up-blast blower assembly on a suitable pedestal may be a better choice. kas