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Choose a solar water heater and protect it from freezing

Solar water heating can supply much of a household's hot water with little or no electricity. The right type depends mostly on how cold your winters get.

How

1. Where freezing is rare, consider passive batch (ICS) or thermosyphon systems, or active direct systems.
2. Where it freezes, use an indirect system with a non-freezing fluid or a drainback system. Use propylene glycol, never toxic ethylene glycol, and plan to replace it every 3 to 5 years.
3. Insulation alone does not stop freezing. Drainback piping needs a continuous slope (at least 0.25 in per ft, about 2 cm per m).
4. Orient collectors toward the equator (up to about 45 degrees off is acceptable) and tilt near latitude, steeper for winter loads.
5. Fit a backup heater for cloudy spells and a high-limit control to deal with overheating in summer.

Safety: Collectors and tanks can exceed 80 C. Fit a tempering or thermostatic mixing valve so scalding water cannot reach taps.

Sources

1. Solar Water Heaters. U.S. Department of Energy, Energy Saver, accessed 2026-11
2. Solar Water Heaters (course R04-016). CED Engineering, accessed 2026-11

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