On Wed, 12 Sep 2007 00:36:28 GMT, Jere Lull wrote:

TW, though I don't believe a small engine such as ours could
practically boil much water --that last degree to flash to steam is a
killer-- it seems a good idea to distill water drawn from the hot water
tank, gaining a good bit of the required BTUs for free.

A BTU is a British Thermal Unit. It is the ammount of heat that it
takes to raise one pound of water by one degree F. It takes about 1073
BTUs to evaporate a pound of water. Roughly 140 BTUs to raise the
water from room temperature to the boiling point. If you are heating
the water in the hot water tank for free, it would help, but not by
much.
There is not really a last degree. The phase change from liquid to gas
takes place at a constant temperature, the boiling point, and and the
last degree of heating below that point, is the same as any other
degree, one BTU per pound. In round figures, seven eights of the
energy goes into the evaporation, one eighth to temperature change.

Boiling point varies greatly with pressure, but I assume that we are
all talking about ordinary sea level, 14.7 psi type air.[give or take
changes with the weather]

Casady