This is a 20-gallon heater from the 1940's. It's made of monel, an alloy of nickel and copper, and unlike today's glass-lined steel tanks, it will take just about forever to corrode and break.

What is unusual about this heater, as opposed to others in this museum, is that it is still being used by an energy analyst in Berkeley, California.

"I am so grateful that the real estate agent didn't toss it out when she had the house painted and "staged" for sale!" she says. "We've never, ever run out of water for a shower, even with it set at 120 F"

The plumbing arrangement on top of the heater was to permit the installation of a temperature/pressure relief valve, something that didn't become code until the 1960s.s