wrote in message
oups.com...
Your idea has merit. Mineral buildup can be a problem in any heat
exchanger using hard water, a car radiator would be no worse and is a
very efficient exchanger. I suggest using your system as a feed into
your regular water heater, it will keep it from having to turn on as
often and will back up any shortfall in your heating system. A
prefilter will remove silt, which helps, but not dissolved minerals. A
water softener will help and will have other benefits but is expensive.
When you build it, consider using a bypass with a Y valve, during the
winter when the attic air is cold ( I don't know your climate), and
during that time you can service it, rinse out mineral deposits with a
weak vinegar/water solution. If you are getting a salvage yard
radiator, get the biggest one you can for the money. Use a simple fan
to boost its efficientcy, wire in a thermocouple to activate it or at
least a timer for the hottest part of the day.-Jitney

I doubt if auto radiators are designed using consideration of maintaining
the water to be suitable for human consumption. They may use lead solder, or
other materials may be used for corrosion resistance that could be dangerous
if consumed.

Bob