A Double-Duty Solar Solution: How to Build a Solar Water Heater

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The author’s solar water and space heater at his home in Montana.
The author’s solar water and space heater at his home in Montana.
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This DIY system collects heat from the sun and uses it to heat water and provide home heat.
This DIY system collects heat from the sun and uses it to heat water and provide home heat.
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To construct the solar collectors, Gary Reysa started with copper pipes.
To construct the solar collectors, Gary Reysa started with copper pipes.
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The next step of building the collector is to install aluminum fins to collect heat.
The next step of building the collector is to install aluminum fins to collect heat.
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Painting the whole assembly black helps it absorb more heat.
Painting the whole assembly black helps it absorb more heat.
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The potable water flows through a long length of PEX tubing submerged within the tank.
The potable water flows through a long length of PEX tubing submerged within the tank.
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This solid, insulated water tank stores solar heat.
This solid, insulated water tank stores solar heat.
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The top layer of the collector is a twin-wall polycarbonate glazing.
The top layer of the collector is a twin-wall polycarbonate glazing.
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The author attaches heat spreaders to his subfloor to improve the heating efficiency.
The author attaches heat spreaders to his subfloor to improve the heating efficiency.

This simple solar water heater provides both domestic hot water and space heating. You can adjust the size and design to meet the needs of your home. You’ll find nearly all the materials at your local hardware or lumber store, and to build it, you need only basic carpentry skills and a little plumbing know-how. Amazingly, the cost of this DIY system is only about one-eighth of what you would pay for an equivalent commercial system!

How It Works

The system takes water from near the bottom of a solar heat storage tank and pumps it through a collector — where it’s heated by the sun — and then back to the tank. This continues as long as there’s sun on the collector. An off-the-shelf controller monitors the temperatures of the collector and the tank, and it turns the pump on only if the collector is hotter than the tank. When the pump is off, water drains from the collector back to the tank. This type of “drainback” system is especially useful in cold climates because it keeps the water from freezing inside the collectors.

Water is preheated in a single pass through a large coil of PEX pipe immersed in the solar storage tank. The preheated water then goes to your regular hot water tank. This simple one-pass system works well because the PEX pipe coil is large enough to hold quite a bit of preheated water right in the coil, and it has so much surface area that it acts as a good heat exchanger after the initial hot water from the coil has been exhausted. The water in the tank is used strictly to store heat — it is not part of the potable water system.

The floor heating system pumps water from near the top of the tank through the radiant floor loops, and then back to the bottom of the tank. The control system monitors the room temperature and the tank temperature, and it turns the pump on only if the room is cold and the tank is hot. The control system is made from two standard thermostats.

  • Published on Dec 20, 2011
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