How to install a whole house fan
Whole-house fans have been cooling homes for about 100 years. The basic concept of a whole house fan has remained the same: A fan mounted in the attic or in the attic floor/living space ceiling draws cool air through open windows and pushes hotter air through attic and roof vents.
The equipment, however, has evolved considerably. Large, noisy fans were once fastened to roof rafters and pulled air through registers in the ceiling. Today, whole-house fans are smaller, quieter and more powerful fans that move more air combined with automatic insulated louvers or shutters that prevent air leakage during colder months.
While a whole house fan uses about 90 percent less electricity than an air conditioner, it may not be practical for some homes, as it can’t cool the house any lower than the outside temperature and doesn’t dehumidify the air.
How to install a whole house fan
Step 1: Sizing the whole house fan
The first step to install a whole house fan is to size it. Whole-house fans are sized in cubic feet per minute (CFM) of cooling power. To get the size for a particular building, first calculate the building’s volume in cubic feet (multiply square footage of the building by the floor-to-ceiling height). Multiply that volume by 30 to 60 air changes per hour (an HVAC professional can help you determine which is most appropriate based on the climate and the building’s floor plan), then divide by 60 minutes to get the cubic feet per minute of capacity the home requires.
If the whole house fan doesn’t come with a tight-sealing cover, consider buying or building one. A tightly sealed, hinged door for the fan opening that is easy to open and close when operating the unit will keep cold air out in the winter and hot air out in the summer.
Step 2: Find the ideal location
The best place to install a whole house fan is in or near a central hallway. Make sure there is enough space around the fan in the attic to ensure good air movement (at least 30 inches minimum clearance from the top of the unit to the roof rafters/trusses). Be sure attic exhaust openings will be sufficient to exhaust warm air. If the attic is closed and vented only through soffit/ridge vents covered by insulation you’ll need to install more venting, i.e. gable-end vents. You need about 1 square foot of net free area for every 750 CFM of fan capacity.
Drive a nail through the ceiling in the center of the fan’s intended location. From inside the attic, remove insulation and make sure there is no wiring or plumbing that will interfere with installation. Cut and remove the sheetrock to fit the unit’s shutter (most units come with a template on the box to get the perfect size). You’ll most likely have to frame a standard opening by cutting one joist and installing two joist-sized pieces of lumber attached to the adjacent joists. For joists with a considerable amount of play or bounce, you may have to add a stabilizer in the center of the opening to reduce rocking during operation.
Step 4: Install mounting hardware and fan
Many units will require a platform constructed of at least 1×4-inch lumber to be placed on top of the framed opening to support all edges of the fan frame. This platform should create an air seal around the entire perimeter of the fan, effectively forming a “duct” from the living space to the fan. Lift the fan through the opening into the attic and set in place. Some units only require partially driving two nails into the platform on all four sides of the frame to pin it in place. Others require screws or bolts be driven through brackets into the platform.
To dampen fan noise and vibration from a whole house fan, fashion gaskets from foam pipe insulation, EPDM rubber, weatherstripping or other similar materials and cushion the platform, brackets, plenums or other attachment points, depending on the fan you are installing.
Step 5: Connect wiring.
To install a whole house fan it is usually recommended that a qualified electrician perform the wiring. A dedicated 120-volt circuit is typically required, and all connections must be secure with no exposed copper conductor. Wiring diagrams are included with all units and are fairly simple once the circuit has been installed at the breaker panel.
Step 6: Make final adjustments.
For belt-drive models, make sure the belt is tightened to manufacturer specs. For direct-drive models, make sure all spindles, gears and other moving components are freely moving and properly lubricated. Install any plenum boards or automatic insulated panels (if included or specified) on top of the fan. Install shutter/grille to the ceiling according to instructions.
Step 7: Test the unit.
Restore power to the circuit, open a few windows and test the unit. Always provide adequate ventilation when operating a whole-house fan by opening windows in several locations around the house. If you don’t, whole-house fans can cause back drafts in furnaces, water heaters or other combustion appliances, pulling carbon monoxide into the building.
Check with local code enforcement agencies and local utilities before you install a whole house fan. They are not allowed in some areas, but qualify for energy rebates in others.
—By Roberto Franco