DIY Window Heaters

Measure the inside of your window with a tape measure. Make sure to include both the top and bottom windowpanes.

Cut a piece of corrugated cardboard to the size you measured. Be sure the cardboard is corrugated by looking for hollow channels located in the middle of the cardboard. If the cardboard is solid, it will not work. The corrugation should run north and south, or vertically, once the cardboard is placed into the window frame.

Paint one side of the cardboard black. Avoid getting any paint into the openings at the corrugation openings at the top and bottom of the cardboard. Allow the paint to dry before proceeding further.

Remove the window screens. This will give the cardboard more room inside the window frame, and will increase the amount of light it receives.

Open the bottom portion of the window. Slide the cardboard into the window frame, black side facing out. The cardboard should rest in between the outside storm window, and the inner glass pane.

Prop the cardboard up with a small piece of paper or a paper clip so the bottom of the cardboard is slightly raised. This will allow air to flow inside the corrugation channels.

Open both the bottom and top windowpanes so they are open about one inch. The airflow from the outside will pass through the corrugation in the cardboard, and will be heated by the sunlight hitting the black paint.