Hello all. Im putting in the 6" round ductwork for a range hood. It will be going through the wall into the garage attic and up out the roof. I could use some advice before i get going. First, the duct pipe will be slightly in contact with a copper heating pipe that runs along the wall. Theres no way around it. What would be the best buffer to put between them? Second, should the pipe run downhill a bit from the hood just in case water gets inside it doesn't flow back to the unit. And last, what is the best way to seal around the pipe at the wall? I researched all this on the net but couldn't find too much info. Thanks for any help.