re: pressurized tank inside of a non-pressurized tank
30 oct 2003
mike p wrote:
>would you explain this concept of a pressurized tank inside of a
>non-pressurized tank to me?
it's easier to build a large unpressurized tank than a pressurized one for
heat storage, because it doesn't have to be as strong. then put a bare
galvanized tank inside the unpressurized one to act as a heat exchanger to
heat potable water for showers and so on. cold tap water flows into the
small tank at about 40 psi and flows out hotter, into the cold water inlet of
a conventional water heater or directly into showers and hot water spigots.
harry thomason heated water this way in hundreds of houses. a single wall heat
exchanger may not be legal under today's plumbing codes. the perceived danger
is that the small tank may have a pinhole, and a fire engine may depressurize
a whole town water supply by pumping water out of a hydrant, sucking non-
potable water from your house into the public water supply. these days, many
new houses have backflow preventers (check valves on the water supply lines.)
a $100 "reduced pressure zone valve" that drains the pipes in a house to
a sump when supply pressure drops may be the next step up in safety.