can you run the duct work to an outside wall inbetween the joists? the motor you pick (along with the recommended duct size) will result in a "maximum recommended duct length" per the manufac. Also, addding 90 bends to the duct will "add" a variable amount of resistance (equiv. to 10 feet of duct length for my 7" installation). again, you might ask a contractor about running the duct between floor joist in the ceiling, to an exterior wall. you would probably need some drywall work on the ceiling, some messing with the cross members between the joists, but it might be easier than running something up to the roof..depends on your layout

I would consider this a low risk worry, but not a negligible risk worry. And there may be an International Building Code or other relevant code violation involved. And I am sure that codes require metal ducting for dryer vents. I don't recall a specific declaration for the termination, but dryer duct fires are a risk that the metal ducting is intended to contain. In commercial settings, the entire exhaust system has to be welded steel. This is to contain grease fires. I haven't read of many kitchen hood vent fires, but that doesn't mean that they can't or don't occur. It would depend on your cooking and the resulting condensation of grease lining the duct. If this is very slight, then the likelihood of propagating a fire to the cap is small. If the plastic cap is not yet installed, _I_ would exchange it for a metal cap. And if you live where snow can accumulate, this cap needs to be high enough that the vent is not blocked. Otherwise, products of gas combustion that aren't healthy might build up when cooking. A blocked vent over an electricity heated stove would only fill the house with cooking effluent, but gas stoves require ventilation for other than aesthetic reasons. kas

Check out the caps at fantech.net

I stand mostly corrected by foodonastump. According to page 31.7 of the 2003 ASHRAE Handbook - HVAC Applications: 'Model building codes, such as the IMC, and standards, such as NFPA Standard 96, have set minimum air velocity for exhaust ducts at 1500 fpm. ... ASHRAE research (Kuehn 1998) indicates that there is no basis for specifying 1500 fpm minimum duct velocity for commercial kitchen ventilation, but rather supports reducing NFPA Standard 96 recommendations to 500 fpm. This change allows flexibility for design of variable-speed exhaust systems and retrofitting older systems, though current design practice for new single-speed systems will generally continue to use design duct velocity around 1500 fpm.' The point here is that at the minimum variable speed setting (for commercial kitchens), the flow velocity should be 500 fpm. Most residential variable speed systems will go down to practically zero fpm, so at those velocities, one would be advised to not be broiling hamburger. Grease effluent consists of various sized particles and vapor. The vapor will not condense out until sufficiently cooled. The particles will either be affected by the centrifugal action of the baffles, or not. In the latter case I think the turbulence in the ducting would have to be extreme to compete with the baffles. I don't have Kuehn's paper so subtleties and assumptions should be checked for relevancy to residential use. A synopsis of the paper's results are available on line. I still need to find time to digest it. kas Here is a link that might be useful: New Rules for Kitchen Exhaust