I have been inspired to make a small step toward capturing and using passive solar heat. Utilizing two south-facing windows in the bedroom and laundry room where the light won’t be missed, I tacked up dark window screening and then nailed a piece of dark paneling to the window frame. I left a small opening at the top and the bottom to encourage airflow.
The thermometer at the top now shows 80- to 90-degree Fahrenheit air coming out, helping to heat the room while saving a few Btus.
Hot Springs, South Dakota