Solar Window Inserts

Step 3 Attach screen to upper vent.

Since we're working with the window screen, let's flip our frame over and attach one layer of screen to what will be the upper outlet vent. This screen is necessary to prevent the flap valve from being sucked into the frame at night. This screen provides a seal for the flap valve so that at night when it's cooling off, your warm air doesn't get drawn into the solar collector and dumped out the bottom vent as cold air.

Just as warming air in the solar panel creates a convection current where warm rises out the top and draws cooler air in the bottom, the reverse is also true. Without some means of preventing reverse air flow through your panel, your warm air would be drawn into the top vent, cooled down, and dumped into your living space, thereby negating any benefits from solar gain collected during the day.