To all, I have been out sick for a few days but am back to working on
my hot water heater. After doing some shopping around and getting with
some plumbers, I have decided just to replace the 50 gal I have with
another 50 gallon. Apparently it is too much trouble / expense to
update my entire vent system from 3" to 4" - - one plumber didn't want
to take the work on, and another very reputable plumber is going to
charge me a lot, so I will just replace like with like.

I have bought a 50 gallon and have a couple of installation questions,
which I will post in a new thread.

Again, thanks to all.

Tim C.