Things You'll Need
12-2 NM cable
NM cable box connectors
Electric cable staples
A thermostat-controlled attic fan is an excellent way to help lower home cooling costs in the summer. When installed properly, this powerful fan can eliminate the hot, humid and stale air that ultimately collects in your attic. If you use your attic for storage, you'll be even more thrilled with the fact that it can help keep your stored items drier and in better condition. Most new attic fans come with thermostats already connected; all you have to do is secure it to the plywood frame and wire it into the circuit.
Screw the thermostat to the attic fan's plywood frame. Ideally the thermostat will be facing the air as it's being drawn out by the fan.
Remove the thermostat cover. You should see a black wire, a white wire and a green ground screw.
Find a circuit you can use to get power to the attic fan. In most cases you can pick up a feed from one of the attic lights, but don't turn the breaker off yet, or you'll be working in the dark.
Run NM cable from the attic fan thermostat to the attic light. Use the hammer and staples to secure the cable to the joists at 12 inch intervals. Staple the cable within 8 inches of both the attic light box and the thermostat box. Leave enough cable at each end to work with.
Use the ROMEX® stripper to cut away about 8 inches of sheath from each end of the cable. Use the wire strippers to remove about 3/4 inch of insulation from each wire.
Remove a knockout from the thermostat box, and install a ROMEX® connector in its place. Insert the wires through the clamp, and tighten the clamp screws down over a sheathed section of cable.
Connect the black thermostat wire to the black cable wire, the white thermostat wire to the white cable wire and the ground wire to the green ground screw in the box.
Install the thermostat box cover, and use the screwdriver to set the thermostat so that the fan will kick on when the attic reaches 105 degrees.
Turn off the breaker that powers the attic light. Wait a few minutes for the bulb to cool off before you disassemble the fixture. Once cooled, remove the fixture.
Remove a knockout from the mounting box, and insert an NM cable connector in its place.
Follow Steps 5 and 6 for bringing the wire into the box.
In the attic light box, connect all of the black wires together, all of the white wires together and all of the ground wires together. Wrap each wire connector with electrical tape, and stuff them back inside the box.
Re-install the attic light, and turn the breaker back on.