the bigger the duct the quieter it will be.
i would use the large duct and use reducers where i had to, or just tape it down. having 6 inches of 6" duct would be better than having several feet. if you blow that big fan through 6" duct, it will only flow as much as the duct can handle..so you might as well have bought a smaller fan.
if you want to reduce 8" just clip the wire in two spots, tape half the duct down pull up the other half and tape that. also cut a few inches of insulation out at the end then pull the end of the wrapper down and tape that as well. looks much better than having insulation hanging all over the place. |