OK now--I'm going to try and convince you that my alternative is still better! I think you should look at a custom Modern Aire liner. You can have them build it to any specs you want, just like your local sheet metal shop. Any size, any taper, any duct size, any lighting arrangement, any switch layout, etc etc, all for a very modest custom upcharge. The advantage, versus your local sheet metal shop, is......they know what they're doing. Consider the baffles. My guess is your local guys will propose using mesh filters purchased from someone. Mesh filters suck (to use a ventilation term). You want baffles. I guess it's possible they would actually fabricate high quality baffles, but I'd be surprised. They are complex enough that I can't imagine a sheet metal shop can make them for a one-off project with any kind of cost effectiveness. It's the baffles that make the hood from my experience--both from a function standpoint, as well as an appearance standpoint. I happen to think that the MA baffles are gorgeous. High quality stainless, with an almost chrome-like finish, yet they can get thrown into the dishwasher and emerge clean and sparkling. They are the professional standard for grease trapping--try to find a restaurant hood that doesn't use baffles. Any other filtering system is suboptimal. Your local guys will either not offer them, or buy them from someone else at an inflated price. Picture isn't great, but you can get a sense of how sweet the baffles look: Baffles are a big issue, but remember too that your local guys will have to source and install lighting, control switching, duct collar, provide a backflow damper, etc etc. I think you're heading towards a project that might save you a few hundred dollars, but will cost you in time and effort, and will end up getting you a hood that is far short in quality and performance of what you could get from a dedicated manufacturer. Your sheet metal guy spends his day fabricating ducts, boxes, brackets, gutters, radiator covers etc etc etc. The Modern Aire factory builds hoods. Just hoods. Just like with choosing your doctor, when you want the best, go with the specialist. PS: I love my MA but it is very important to point out that there are other custom hood manufacturers who build equally great custom hoods too. I'd spend a bit more to get a hood from any of them rather than roll the dice on a sheet metal shop.

Yikes! Your troll is accepted. First, I suggest as an appetizer you tour the blower section of Fantech's website (www.fantech.net) followed up by a maincourse on fan types (that I think is) at Ametek/Rotron's site (www.rotron.com), and for desert, tour Greenheck's site (www.greenheck.com) for a commercial perspective. There are actually several types of filters, but for most residential products there are two distinguished by function: centrifugal and impact. The Vent-a-Hood squirrel cage blower slings the grease particles against the blower housing wall by centrifugal action. Baffles sling the grease against their own structure due to rapid reversals in flow pattern. Meshes, ball bearing packs, fiber packs, etc., use impact. Not so residential types include intense UV to oxidize the grease into inert CO2 and carbon (and probably other stuff). There are motors and then there are fans. Taken together we can call them blowers. A vane-axial fan is a type of blower and comprises a housing, a motor, and an axial fan blade set. (That is, the blades are axially symmetric but mounted radially.) A centrifugal fan can be squirrel cage type like the VAH, or more like the flat plate with upright blades design Wolf uses for its roof fans (made by Broan). Open-tip bladed designs (propeller fans) like floor and table fans can also be used, and may be found in the smaller sized vent paths such as in OTR microwave ovens. Whole house ventilation fans in my experience are propeller fans but usually have a surround duct making them intermediate to vane-axial fans. A true vane-axial fan allows little air spillage off the blade tips by closely fitting to the surround. High bypass turbojet engines are of this type. Most of the motors one will find are induction motors, one motor design out of the many that have been invented and used over more than a century. They can be single phase or higher number of phases, but the latter are usually industrial or aerospace oriented. The type of motor/blade configuration that a particular hood utilizes needs to be determined for each hood of interest if one cares; assuming that the squirrel cage type will be found inside may not be valid. I should note that the function of baffle and mesh filters is to remove as much as practicable of the grease particle spectrum before it can impact the fan blades and duct walls. This is the larger particle part. The finer part of the spectrum is (ideally) kept as an aerosol and vented into the atmosphere. I have used kitchen ventilation for a long time, albeit not at the scale I have now, and in general the amount of grease that attaches to ducts and the roof mounted exhaust fans is very low considering their length of time in use. Fans within hoods with less than ideal baffles or mesh filters will collect some grease, but in most cases, even with VAH with no filter, most is slung off. It is the walls around the fan blades that one has to investigate for cleaning, or in the case of VAH, plan on cleaning. kas P.S. Language is invented as an aid to concept communication, and in technical fields "technospeak" is necessary to avoid ambiguity and shorten necessary unambiguous communication, just as math symbolism and rules similarly but even more compactly simplify describing things mathematical.

The easiest way for them to run duct in a two-story house is between the floor joists in the ceiling above. Well, the easiest way is probably to run through upper cabinets, if you have them. You need to figure out which way those ceiling joists run - look in an upstairs register or at the joists in the basement or attic to get a good guess. If they go the right way your ducting could go up from the hood to the ceiling, turn a right angle to go between the joists, and go out through the wall. We had a guy from a fireplace shop come and look at our house. He had good suggestions for how to get to the outside from an interior wall, and it wasn't what we thought it was going to be, mostly because the joists ran in an inconvenient direction. We were ballpark-quoted in the $1000 neighborhood to go completely across the top of the kitchen and out the opposite brick wall, plus a second run of duct in another place, through another brick wall, for make-up air (required for a 401+ CFM hood in our area). I believe if we only had to do the single run, it'd have been about half that. Material costs are very low and the hard work in our case was getting through the masonry. Note that our estimate did not include patching up the ceiling after they cut a bunch of holes in it. We also have a recirculating microwave-hood and we hate it. The diffuser piece at the top on ours has broken so I get the breeze right in my forehead as I stand at the stove. We can't wait to have a proper outside-venting hood!

That hood will perform very poorly. If this will be over induction and nothing more than boiling water you'll be OK but otherwise I'd avoid it.