[QUOTE=cybermuda;338549]see "Passive Hot Water Heat" under the DIY section
That also sounds neet but this was a manufactured unit that us not so handy folks could have installed right on a hot water heater to augment or replace most of the cost of the gas or electric heating of the water by a professional. It is suppose to be a scaled down version of a heat pump like you use to heat a house. I had solar hot water when I lived in California and loved it but this old house article said this cost something like $450 which is a far cry from the cost of solar.
I have to stop reading the articles that this old house emails me links to as I already have more projects than I can finish,