"Bill" wrote in message

So guess what? The metal chimney going straight up will go right smack dab
through a rafter (45 deg. roof slope - one of many 2 x 4's at 45 deg.
angle
supporting roof.)

So I will need to cut the rafter....

There are ways of boxing around the stack, but it may be easier and cheaper
to buy a couple of 45 degree elbows and zig around hte 2 x 4.