Whole house fans are a great way to save energy in the summer, but if left unattended during the winter months, they can be a drain on your energy budget.

For optimal energy efficiency, both the louvers and the fan housing need to be insulated.

If it is too difficult to access the fan housing in the attic, insulating just the fan louvers is a good option.

Step 1: Pre-made louver covers are available from some manufacturers, but simple plastic sheeting will do an excellent job of keeping warm air in and cold air out.

Choose 4 mil or 6 mil clear plastic sheeting or purchase a package of shrink wrap window film large enough to cover the entire louvered opening.

Step 2: Cut the plastic sheeting one to two inches larger than the louver opening.

Step 3: Install removable double-sided clear tape along the full perimeter of the louvers.

Step 4: Press one edge of the plastic sheeting onto the double-sided tape along one side of the louvers.

Step 5: Pull the plastic taut and continue to press the sheeting up along the edges of the louvers.

Step 6: Pull the plastic tight and press it into place along the center of the other two sides. Continue to press the plastic into place until it is completely adhered around all edges.

Step 7: For shrink wrap applications, use a hair dryer to heat the plastic until it is taut and virtually invisible across the louver opening.

Step 8: Trim the loose edges of the plastic for a clean, weather-tight cover.

Step 9: If the fan housing is accessible on the attic side, climb into the attic and turn the fan’s safety switch to the “off” position.

Step 10: With gloves on, cut bats of insulation into small sections and press the insulation pieces down into the fan housing.

Step 11: An alternative to stuffing the fan with insulation is to build an insulated box to cover the fan. Select a sheet of 1-inch-thick Styrofoam and use a carton knife to cut a square slightly larger than the fan housing.

Step 12: Cut four sides to match the cover and assemble the box with a good-quality duct tape.

Step 13: Place the box over the fan housing and run a strip of duct tape between it and the floor for added weather protection.