My 6 year old Rheem 50 gallon gas hot water heater is seeping water out
the top and about to die. The warranty expired last month, of course.
It is installed in a corner of my garage and vents out the roof of our
second story house. We have 3 1/2 baths and a family of 8 and often
run out of hot water. We are considering upgrading to a 75 gallon gas
model, with higher BTU and larger first hour recovery specs.

I have found a number of places that sell 75 gallons models, home
depot, sears, lowes, and many different brands, etc. No one seems to
have 75 gallon in stock since it is not a common size, and all say 2 -
3 weeks to special order.

Most of the specs list a 4 inch vent. Currently I have a 3 inch vent
as far as I now. Does this mean the vent size all the way up and
through the roof will have to be upgraded? or can it just be adapted
above the heater from 4 back to 3 inch? I assume that would be unsafe
and violate some codes.

I have thought about a tankless but have pretty much ruled that out due
to higher initial cost and concerns about its ability to keep up with
my family's usage patterns.

Does anyone have any advice on how I can get a 75 gallon in short
order? or any suggested alternatives or advice? I like traditional
gas hot water heaters and I am relunctant to try anything unusual.
Thanks,
Tim C.