Battening Down the Hatches for Winter

Last winter, we had an energy audit performed by About Saving Heat of Denver. The technician had a neat gizmo that automatically measures the air temperature, similar to the instant read thermometer you use to make sure your chicken is cooked properly. Anyway, when he held the machine to the ceiling and passed it over the air conditioning vents - closed for the winter, of course - the temperature was two to three degrees cooler, meaning that cold air was still leaking through the vents. He recommended a simple and inexpensive fix, magnetic vent covers: