Thanks John.
Some have suggested NOT to use a hole saw but instead a jig saw or sawzall.
Mostly because of tearing through roof shingles once it pokes through.
Thoughts on this?


The hole through the roof will not be round, but an oval due to the slope of
the roof. The higher the slope, the longer the oval. I just hold a piece of
pipe vertcally in position on the underside, and trace the outline with a magic
marker, this will give a nice clearance. You can start with a hole saw, but you
will need a drill with a side handle to hold one that large. I only use a heavy
duty angle drill for holes this large. Better to use the jigsaw.

Drill a couple of locating holes from the underside, then go on the roof and
mark the oval by placing a piece of ductwork vertically and tracing again. Cut
away the shingles with a razor knife, than cut the hole with the jigsaw. The
hole throguh the shingles will be larger than the one through the roof, so that
the flange of the flashing will fit.

--
Dennis