The easiest way to winterize an attic fan (also known as a whole house fan) is to install a shutter seal over the shutter. While an attic fan provides necessary cooling during the warmer months, any unprotected opening in the ceiling lets heat escape when heating the home.
Installing an attic fan generally makes a hole of around 16 square feet, or even bigger, in the ceiling, as well as removing any insulation that protects the living space below from the temperatures in the attic. This means that a shutter is the only thing separating the people in the home from the temperatures above that hole.
Purchasing a shutter seal changes the shutter from a hole to an extension of the wall. It is possible to have the seal trimmed to fit the shutter and to secure the seal in place with Velcro. This sort of seal also works to insulate and seal air conditioning vents. When the warm weather returns and it is time to run the attic fan, taking the seal off is simple. Combining this sort of winterization with covering dryer exhaust ducts and protecting the damper in the chimney can contribute to significant savings on winter heating bills.