The U.S. Department of Energy recommends covering older models of whole house fans when not in use.
A typical older whole house fan has a 30-inch-diameter blade with a sheet metal cowling of 31 inches to allow for blade clearance. An attic-side box cover may be constructed from a 4-by-4-foot piece of 1-inch rigid fiberglass duct board.
The box will be 33 inches square with 1-inch-thick walls (inside dimension of 31 by 31 inches). It will be 6 1/2 inches deep. Adjust the dimensions if you are purchasing a newer whole house fan.
Box cover materials list:
* 48-by-48-inch piece of 1-inch fiberglass duct board
* Silver duct tape or house wrap tape
* Measuring tape, straight edge, utility knife
* Permanent marker to label box
* Gloves and eye protection
* H brackets
When installing a whole house fan, be sure to provide proper support and seal the unit into the rough opening in the ceiling. Never cut a truss chord; wooden H brackets installed between the trusses create a framed box to raise the fan above the truss system. The louvers must be able to operate freely, and care must be taken to prevent binding or misalignments.
See more about whole-house ventilation and fans:
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