Typically, the most efficient and quietest systems are ducted to a
roof fan where the motor is in the roof mount. We just did our
kitchen over and used a 10" OD round duct fitted to a Wolf
commercial-style (but residential design) hood and roof duct. The
setup is 900CFM and we have a five-burner gas rangetop. I honestly
forget what the BTUs are, but another concern is having the hood not
too far from the source of the heat/steam/grease/etc. and of course
not too close either. I don't think you can build a very efficient
system within the confines of a 2X4 wall. If you had 2X6 that might
help. BTW, the hood we have is Wolf Pro Hood 36":

http://www.wolfappliance.com/Ventilation/ProWallHood

The Range is the following:

http://www.wolfappliance.com/GasCook...T36GGasCooktop

I have to also note that my wife absolutely loves this setup. Cleaning
the solid stainless steel hood louver modules is easy... lift the
module and pull it out of the frame, pop in dishwasher and the
reinstall. Same as in my son's restaurant.

On Wed, 06 Feb 2008 22:23:04 GMT, (Una) wrote:

The NuTone website recommends min 1 CFM per 100 BTU; is that BTU of the
highest BTU element, the total BTU of all elements, or the total BTU you
are likely to use at one time?

Can the "out the back" rectangular duct be run inside a wall? 3.25x10in
should fit in most walls, if framing is at least 2x4 and 12in or greater
on center. That would involve a turn, from horizontal to vertical, but
would save the cabinet over the range.

Una