How long does YOUR water heater endure? These are several designs made to last. They are tank-type heaters that have tanks made of copper or monel (a copper-nickel mix) -- no anode needed.
In normal water, they can last a lifetime. Sadly, tanks like this are no longer made.
Several of these have external flues. That means that instead of a tube carrying hot gases up the center of the tank, as in most of today's models, the gases flowed between the wall of the tank and the exterior shell, thus creating a far greater surface area for heat exchange.
And, it was possible to dome the bottom of the tank down. This made it possible to remove sediment easily with a drain valve if it were attached at the lowest point at the bottom center of the tank. Again, this would make it easy to maintain the heater, adding to its life.
A: Ruud Monel, early '50s, 20-gallon tank, still works. Disconnected because the installer didn't understand the control. External flue.
B: Whitehead Monel tank; external flue. Late '40s.
C: General Supreme 40-gallon copper; external flue. Mid-'50s.
D: Mission heater, late 40s, standard flue, unknown alloy, steel tank, not glass lined; offset flue.More Fun Stuff