Jmagerl wrote:

In the five homes I've owned over the last 30 years, I have never had an
expansion tank on the hot water heater. My daughter just bought a home (new
construction) and it has one. Did something change? Do I really need one?
It seems to me that any expansion of the water in the tank would just be
pushed out the cold water inlet and pressure wouldn't increase. What am I
missing?



Places with high city water pressure will have a Pressure Reducing
Valve to lower it. By design, these valves block flow to the street
(some exceptions). Also, many localities now require backflow
preventer valves (check valves). All these situations are required
to have an exp tank today.

http://www.stateind.com/expansion/expansion.htm


Jim