Homemade Solar Window Heater

Locate an unshaded, south-facing window in your home, because that will provide the appropriate exposure for utilizing a solar window heater. Measure the height and width of the window using a tape measure.

Measure a piece of corrugated cardboard to the same dimensions as the window. Add 5-inch-tall flaps to each side of the corrugated cardboard. Cut out the cardboard with scissors.

Lay the cardboard on a large, flat work surface. Coat the cardboard with gesso or primer using a large, flat paintbrush. Allow the gesso or primer to dry thoroughly before proceeding.

Paint over the gesso or primer with matte black paint. Paint only one side of the corrugated cardboard. Make sure the paint is applied evenly and the coat is thick. Let the paint dry completely.

Cut out three square vents measuring 3 inches by 3 inches along the top and bottom of the cardboard using a utility knife. Space the vents evenly at the base of the top and bottom flaps.

Press thumbtacks into the unpainted side of the cardboard along the top and bottom of each vent. Position the thumbtacks so the first vent has two thumbtacks along the bottom and one centered at the top. Alternate the orientation of the thumbtacks at each vent.

Wind string between the top and bottom thumbtacks to create a zigzag pattern over the vents. Tie off the string. Secure the thumbtacks with small pieces of duct tape to keep them secure.

Cut a piece of plastic wrap large enough to cover the vent units at the top and bottom of the corrugated cardboard. Secure the plastic wrap over the bottom vents on the black side of the cardboard and to the upper vents on the unpainted side of the cardboard. Use duct tape to secure the plastic wrap.

Lay the cardboard on its unpainted side. Lift the flaps around the edges. Secure the corners in the upright position using masking tape. Use more than one layer of tape to ensure the corners are sturdy.

Open the south-facing window 1 inch at the top and bottom to create suction, which will push air into the unit. Push the cardboard into the window with the black side facing out. Push it in until the back is flush with the edges of the window. Secure the solar window heater to the edges of the window with masking tape.