exhaust venting

7echo

The remodel will include something we haven't had- a range hood. When I had the roof replaced 4 years ago I asked for a vent to be installed so we would be ready for the range hood. I didn't really think about it at the time, but now I have questions.

The vent is a 6" duct and the cap is only a few inches off the roof deck. The gap from the cap to the deck is only a 3 inches, +/- . Is this too close to the deck?

The range hood has a 7" round option(vertical), or a 3.25" x 10" rect. option. I can use either, is one better than the other?

Will there be much problem reducing the 7" hood duct to match the 6" exhaust cap? Or should I get some pricing on enlarging the exhaust duct?

BTW, the roof is a torch down membrane. Pitch might be about 3 in 12.

Thanks!

Gary in WA

I'd check with the hood manufacturer before reducing. The round is better. 3.25x10 = 32.25 7x 3.1416 = 21.99 or 10+ smaller, yet manu. says either. The round is 33% less surface area for grease to accumulate on and easier to work with. Three sheet metal screws at each joint, try to use 45* elbows instead of 90*. Tape all joints and elbow joints with foil tape, and support duct work securely. I'd pay a roofer to install the correct terminal cap:
http://www.lowes.com/lowes/lkn?actio...1CM&lpage=none
Check with him if proper one. Be safe, G

7echo

Thanks for the comments, I may talk to a couple of roof guys and see what sort of money they want to do this job.

Can someone point me to examples of, or instructions to, properly flashed roof exhaust caps used with torch down roof membrane?