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Old 01-14-11, 09:35 AM   #9
Piwoslaw
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Unless you find laws which state that your heat exchanger must not only be double walled, but also certified, then you can try to make your own. For example, instead of making an open solar loop that dumps into the non-pressurized tank, make the solar loop closed and use that tank as the double walled heat exchanger, something like a heat buffer. That way you can use glycol in the solar loop (to prevent freezing) and still keep it two walls away from your city water.

If you want/need to keep the solar loop open, then get a hot water tank with a (single walled) heat exchanger loop inside and hook that up to the loop in the non-pressurized tank.

Or go a step further and replace your hot water tank with a heat buffer. It should be a tank with two coils - one for input, one for output - while the tank itself and all of its water only act as heat storage (and as double walled heat exchanger).
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