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.

I'll try it with you celticmoon. And we'll see. I also noted that only one of the two cages was dirty (although I did wash them both). It was the white one. It was pretty disgusting, it had to go through the dishwasher twice. Must be because I don't use the supplementary "boost" or whatever button. So I may be able to at least get away with only dealing with one squirrel cage. I wonder too, if I do it often, I can keep it relatively clean without taking it down? We shall see. I also note that the paint came off the white one in the wash. Ah well.

As a frequent poster to the appliance forum I have posted regarding VAH on numerous occasions. To sum it up. I don't love my vent-a-hood, but also do not hate it. I used to have a 30x24x18 professional series VAH over a 30" Viking AG range. It worked ok, captured most of the smoke/grease but I thought it was kind of loud. In my new home I have put a 54x27x18 (1200cfm) professional series over top of my 48" Bluestar RNB with grill and griddle. I can tell you that this hood sucks up absolutely everything I can throw at it, whether it is woking up a smoke storm or BBQing steaks on the grill. However I do find it to be loud. It is not deafening, but there certainly is quieter out there. If you have the stomach, take the cover off the sqirrel cage after doing some heavy duty woking etc, and just look at the grease it has captured. It honestly is revolting, BUT it is doing it's job. I just throw them into the DW and they come out all clean and ready to capture more impurities. So, would I buy a VAH again? Hmmmm.....I think I would look into other options a little closer, but I do know that these things work, and their cost is not all that bad either. Plus it does come in a 27 inch depth which I highly recommend. So, yes I would buy one again....maybe :)

The roofers (reputedly the best n my area) did the installation last week which turned out to be a less than 2 minute job. I poked a hole through the membrane where I wanted the hole and the roofers found a suitable spot close by. The 8" flange fit right between two battens (what holds up the roof tiles and what they hang from) and two adjacent tiles. Overlays enough so the roofers think it shouldn't leak. Easy enough to close up by replacing the tile if it does. The 1" flange is rather short so screwing in the elbow was a PITA. The roof vent may actually be stainless steel the more I look at it. Looks more like the stainless steel used in the VaH warming shelf than the galvanised ducting I used.