DIY Solar-powered Window Heater

Cut two 3-foot-9-inch-long sections from one of the 2-by-6 boards. Screw the end of one of the lengths of wood to the inner edge at the end of one of the long boards so that they create a 90-degree angle. Attach the remaining board to the other end of the short one. Attach the remaining short board between the other ends of the two longer boards.

Attach the 4-by-8-foot sheet of 1/2-inch plywood to the frame, placing the screws about one foot apart from each other. Turn the frame upside down so it makes a box with no top.

Cut out a 4-foot-9-inch-by-7-foot-9-inch sheet of metal with the metal-cutting shears. Use the work gloves when cutting metal because the cut edges can be as sharp. Coat the inside bottom of the box with epoxy, and then put the sheet of metal on top. Allow it to dry out thoroughly before continuing. Use epoxy here, as the screws would stick out of the bottom.

Drill a hole in the base of the box in the left-hand corner of either of the narrow ends. Make the hole as wide as the flexible duct. Put one end of the long duct into the hole and seal it in place with the epoxy. This end of the box will serve as the bottom end of your solar heater.

Drill another hole in the right corner of the other end. Make it as wide as the duct. Insert the duct into this hole and epoxy it in place. This end will serve as the upper end.

Place one end of a 3-foot-long 2-by-6 board against the left-hand inward wall of the frame, 2 foot 8 inches up from the lower end. Screw it into place.

Place one end of the other short 2-by-6 against the right wall, 5 feet 4 inches from the bottom. Screw that one into place. These boards serve as baffles to give the air a longer, winding path as it rises, which gives it more time to heat up.

Paint the whole assembly black, both inside and outside. Epoxy the acrylic sheet to the top of the bottom end of the heater.

Cut a small sheet of plywood that is as long as the width of your window and broader than the ducts by a couple inches. Drill two holes in it that are as wide as the ducts.

Open a window on a south-facing wall. Put the piece that you just shaped into it and clench it into position by lowering the window against it.

Lean the top end of the heater on the windowsill, and run both of the ducts into the house through the holes in the plywood. The duct from the bottom end of the device should sit close to the floor.