A powered attic fan can provide attic ventilation all year round. It will lower your cooling bills in the summertime by removing superheated air from your attic where temperatures can reach dangerous 160 degrees. In the winter, a powered attic fan helps keep the air drier by removing humidity that can damage the wood and your roof. A powered attic fan effectively acts as an exhaust fan for your whole house.
Installing Power Attic Fans
Wiring powered attic fans is usually as simple as running power from the existing attic light fixture. If you need to create a new hole for the fan, the wiring may actually be the easiest part. It is critical to install the fan in such a way that seals openings and leaks around the fan itself. Installing the fan in a preexisting hole is your best bet and can often be accomplished by removing a plain grate vent and installing the fan in its place.
Installing a power roof fan can be a dirty job. Take safety precautions such as wearing goggles to keep dust and debris out of your eyes. You'll also want to wear long sleeves to protect yourself from insulation. Fortunately, many powered attic fans come in a kit that includes everything you'll need to install the fan, including a traceable template that will assure a good fit between the fan and the hole.
Fan Thermostat
Like your heating and cooling system, an attic fan comes with a thermostat. The thermostat is mounted with the fan and can be set to automatically turn the fan on when a certain air temperature is reached. It may also have a controller such as a remote control that allows you to turn the fan off and on at will. Using the automatic settings to run the fan when the temperature climbs is a no-worry way of controlling your energy costs and preventing roof damage.
Wiring Power Attic Fans
If you have any doubt about wiring, hire a professional to install your fan. If you're familiar with wiring, first cut the power to your attic light and then connect Romex wire that's been stripped of about 8 inches of covering at the end to an available knockout in the junction box. Then run the wiring to your attic fan, strip another 8 inches at that end and connect the wire to the thermostat. Strip away about 3/4 inch of the insulation and use a wire nut to connect all the white wires. Then wrap the green wire around the grounding screw inside the thermostat box. Connect the black wire coming from the light fixture to the black wire on the box, then connect the red wire on the thermostat to the black wire that comes from the fan motor.
Rewire the Light
Take the spool of Romex and cut lengths 6 inches long of black, white and ground wire. Make a "pigtail" of each of the white, black and ground wires by using a wire nut for each of them. Then install these pigtailed wires to the light fixture in the same way the wires you removed were installed.
For safety's sake, staple the Romex wire coming from the light fixture to the ceiling joists, or at least every 12 inches. When you're finished with the wiring be sure to wrap all the wires with electrical tape. Now set the thermostat to 95 degrees and your powered attic fan will turn on to keep your attic a safer and more energy efficient temperature.
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