"Bob M." writes:

"blueman" wrote in message
...


Specifically, we have a 40 gallon gas-fired water heater on city water
with 3/4" inlet and outlet to the water heater and copper plumbing
throughout the house. We have 4 bathrooms and a kitchen. The city
water pressure comes in at about 85 PSI.

85 PSI is pretty high, you may want to invest in a pressure reducing valve.

How important is it to add a thermal expansion tank or is this one of
those "if it ain't broke, don't fix it" kind of things?

Depends on your city water system. Do they have an anti-backflow valve
in the water meter?

I am not aware that there is an anti-backflow valve though I imagine
it could be built into the meter (which is one of those electronic
ones that they then broadcast wirelessly). Is there any easy way to
check by looking or would I need to call the city and/or try to find
and look up a model number.

If yes, then you must have an expansion tank
otherwise the T&P valve on the water heater will get a lot of
use. Water expands when it's heated, it has to go somewhere.

If there's no anti-backflow valve in the system, don't bother with an
expansion tank.

Makes sense...