In article , Speedy Jim wrote:

snip

So; can an amateur replace these valves without too much trouble? SNIP

Find out what the pipe size is from the meter into the house;
that will dictate what size reducing valve (PRV) to get.
As RikC suggested, making a pressure measurement needs to be
done first. You can buy an inexpensive gauge to mate with
a hose bibb.

If street presure is below, say 80 PSI, there may be a check
valve or backflow preventer which is making the expansion tank
necessary.

One expansion tank may not be enough for TWO water heaters;
the tanks are sized by gallonage because that controls the
amount of expansion. I would rather have 2 separate expansion tanks.

Couple of links:
http://www.flexconind.com/html/wh-series_.html

http://www.wattsreg.com/


Jim

Thanks to RikC & Jim; between the two of you, I have a picture in my
mind of how to proceed. And woe unto me for saying anything defamitory
about our HVAC guy, who DH has known for nearly twenty years (and DH & I
haven't been married for three years, yet).

I understand why it might be preferable to have two expansion tanks, but
I know that thought was given to the size of the tank to handle both
water heaters. I also understand that valves can go bad for different
reasons and that none of them have anything to do with the HVAC guy. So,
I am pulling my plumbing basket out and getting ready to go over to the
double to so some measuring and I'm bringing the digital camera so that
when we go to the plumbing shop, the guys know what to tell me.