- 1). Cut two 3-foot-9-inch-long boards out of one of the 2-by-6 boards. Screw the end of one of the short pieces to the inside edge at the end of one of the long boards, so they make a right angle. Screw the other long board to the other end of the same short board. Screw the remaining short board inside the other ends of the two long boards. You should now have a rectangular frame 8 feet long, 4 feet wide, and 6 inches deep.
- 2). Screw a 4-by-8-foot sheet of plywood to the wooden frame, spacing the screws about 1 foot apart. Turn the frame upside down, so that it is a box with an open top.
- 3). Cut a 4-foot-9-inch by 7-foot-9-inch rectangle of metal, using the metal shears. Wear gloves when cutting metal, as the cut edges can be sharp. Coat the inside bottom of the box with epoxy, and put the sheet of metal on top of it. Allow the epoxy to dry. Use epoxy here because screws would poke out through the plywood.
- 4). Drill ½-inch holes in the bottom of the box, at both narrow ends. Drill holes every 4 inches, beginning 4 inches away from each narrow side and all across the width of the box, from one of the long sides to the other.
- 5). Paint the box black both inside and out, including the metal. Allow the paint to dry.
- 6). The solar heater is now ready to be attached to a south-facing wall of your house. Cut vents in your house wall matching the holes drilled in the box. Attach the heater to the side of your house by screwing it into the wall studs through the bottom of the box. Cut a 4-foot-by-8-foot sheet of plexiglass, using the hacksaw. Set it on top of the box, drill guide holes for the screws about every 1 foot, and screw it in place.