Hey, I thought this discussion in another board might interest some folks here. Its about the use of add-on air source heat pumps for heating domestic hot water. I believe the units discussed work using your existing tank-type water heater.
Cheers.
http://www.hearth.com/econtent/index.php/forums/viewthread/33869/
Replies
Using an air-source heat pump for hot water heating puts into the water both the electrical energy used by the device and several times that amount as heat from the air surrounding the device. If it is within conditioned space, then the now cooler surrounding air must be reheated by the house's heating system. OK, that system may provide heat less expensively than electric resistance heating. But why not just use a propane/natural gas hot water heater in the first place?
If you are in an air-condition dominated climate, then there is an advantage, as the heat being removed from the air inside the house is rejected to water you want heated rather than wasted outside.
Agreed on where the heat goes or gets taken from. I heat with a wood stove in the basement in the winter so I'd effectively be heating my DMH with wood. In the summer, I can use the air conditioning and dehumidifcation in the basement. Natural gas is unavailable and propane is expensive relative to electricity (per unit heat) where I live.