Plan the Heater
Using a compass, find south and north. Your solar pond heater must face south, where the sun’s rays hit it for at least six to eight hours a day.
Measure the space available. Depending on the location, the pond heater should be a minimum of 16 square feet, i.e., 2x8 feet or 4x4 feet.
Measure the existing pond pump intake and out hoses. The size of the pump hose determines the size of the garden hose or tubing to use in the heater.
Scavenge or purchase the materials. Free online classified ads are good sources for free lumber, plywood and other materials.
Building the Pond Heater
Cut the plywood to size. Drill a hole in the center of the plywood, large enough for the hose to go through it. Lay the plywood flat. Cut the 1x2s to size, making a frame around the outside edge of the plywood. Leave a gap wide enough for the hose on the bottom corner of the frame. Screw the 1x2s to the plywood, using 1½-inch deck screws.
Paint the entire unit, both sides, with at least two coats of flat black exterior house paint. If black clashes with your garden décor, use a very dark color like purple, midnight blue or dark forest green.
Wind the black hose inside the frame, with one end through the hole in the middle and extending at least a foot below the bottom of the frame. Wind in a circle, much like a braided rug, until the frame is full. Do not kink the hose; wind it loosely so the water runs freely through it. The remainder of the hose extends outside the frame, through the space you left in the bottom corner.
Lay the plastic sheeting over the frame. Carefully stretch it tightly over the hose and staple it all the way around the frame. Fold the corners and trim to fit. Staple several times to secure the plastic.
Installing the Pond Heater
Lean the pond heater against a fence or the house so that the entire structure is at about a 70-degree angle. You can also mount the heater on a sturdy fence.
Attach the hose, using adaptors if necessary, to the pool pump. The pond water runs through the pump first, then through the heater, returning warm water to the pond.
Turn the pump on and check for leaks.