Installing an attic fan

MATERIALS: Attic fan, cable with clamps, wire nuts, electrician’s tape

TOOLS: Drill, fish tape, screwdriver, lineman's pliers, combination stripper

Temperatures in an attic can reach 150 degrees in the summer, making it difficult (and expensive) to keep a home cool. An attic fan, a whole-house fan, or a roof fan slashes energy costs and reduces temperatures. The manufacturer should provide a chart detailing how powerful a fan you need based on the size of your attic. Depending on the size of your house, you may require more than one fan.

If your attic doesn’t have a louvered opening as shown in step 2, you will have to install one. They can be purchased at home centers.

1 BRING POWER INTO THE ATTIC. Before tapping into a receptacle or junction box for power, check the amperage on your attic fan and make sure you will not overload the circuit. Shut off power to the circuit. Check with local codes to see whether you need to use armored cable instead of NM cable.

2 MOUNT THE FAN. At a louvered opening in the attic, secure the fan by driving screws through its mounting brackets and into studs. If the studs do not allow you to center the fan in the opening, attach horizontal 2x4s that span between the studs. Attach the fan to the studs. You may choose to install louvers that close when the fan is not operating.

3 MAKE THE ELECTRICAL CONNECTIONS. The fan has its own thermostat switch. Mount the thermostat box to a framing member. Follow the manufacturer's instructions for connecting wires. Restore power and adjust the temperature control. Or, you can control the fan with a switch located in a downstairs hallway.

AN ATTIC MUST BREATHE - An attic fan, whole-house fan, or roof fan moves air efficiently only if the attic is properly ventilated. Usually a house needs vents near the bottom of the attic (usually under the eaves) and vents near the roof peak, such as turbine vents, gable vents, or a continuous vent running along the ridge. Check that eave vents are not clogged with insulation. If you are not sure that your attic is properly vented, have it inspected by a professional roofer.

A well-placed attic fan that ventilates effectively can reduce your overall cooling costs significantly.

Installing a whole-house fan

MATERIALS: Whole-house fan, screws, junction box, switch box, cable with clamps, wire nuts, electrician's tape

TOOLS: Stud finder, drill, ladder, saw, combination stripper, lineman’s pliers, screwdriver

Find a powerful yet quiet whole-house fan to pull up air through the house and into your attic. A whole-house fan is ideal for spring and fall cooling in hot climates; it may be the only method of cooling you need in moderate climates. For the fan to work, the attic must have adequate ventilation, and windows on the first floor must be open. Measure your home’s square footage to choose die right size fan. It takes as much time and effort to put in wiring for an undersized fan that will not cool your house as it does to put in the right fan to be comfortable.

1 CUT A HOLE. Fans are designed to be positioned over one joist so you don't have to compromise ceiling framing. Use a stud finder, then cut a 1'x2' finder hole to confirm that the fan will center on a joist. Mark the cutout for the louver and cut through the drywall or lath and plaster. The fan manufacturer will specify dimensions for the hole.

2 BRING POWER TO THE FAN. After making sure that you will not overload a circuit, shut off power to the circuit. Tap into a junction box or run cable up into the attic. Local codes may require you to use armored cable instead of NM cable.

3 WIRE FOR THE SWITCH. A fan-rated rheostat switch lets you vary the fan speed. Bring the two-wire switch cable to the box, marking the white wire black at both ends. Splice it to the black wires in the box. Splice the other switch wire to the fan's black wire and the fan's white to the white wires in the box. Connect the ground.

4 MOUNT THE FAN. With a helper, lift the fan up through the opening and into the attic. Add 2x4 framing as needed so that the fan is securely centered over a joist. Attach brackets to the fan frame and position them so they will slip over the exposed joist. Center the fan over the opening and secure the brackets with bolts.

5 ENCLOSE THE FAN. Pullback the insulation and cut pieces of 2x4 blocking to fill gaps at either side of the fan. At each side, cut two pieces to fit between the joists (shown) or one notched piece that fits over the joist. (Some manufacturers supply blocking.) Attach the wood to the joists by drilling pilot holes and driving 3-inch screws or 16-penny nails.

6 WIRE THE RHEOSTAT SWITCH. Install a fan-rated rheostat switch in the hallway, connecting it to the cable you have run through the wall from the attic junction box. Wire as shown or use the manufacturer's directions.

7 ATTACH THE LOUVERS. Hold the louver panel against the ceiling so it covers the hole. Attach the panel by driving screws into the joists and blocking. Restore power and test the fan.

A ROOF FAN WILL PULL THE AIR OUT OF YOUR ATTIC - If your attic does not have a vertical wall to accommodate an attic fan, this is the next most efficient way to pull air out of an attic. The most difficult part of this installation is not the electrical work, but cutting the hole and properly sealing the roofing around the fan. The shingles must be laid correctly over the fan flashing or the roof will leak. Call a roofer if you aren't sure how to seal the fan. If you are uncomfortable working on the roof, hire a professional.

Choose a spot for the fan that is between rafters, because they are structural elements, they must not be altered in any way.

1 CUT THE HOLE AND ROOFING. Follow the manufacturer's directions for cutting a hole through the roof and for cutting back shingles from around the hole. Carefully fold back the shingles.

2 INSTALL THE FAN. Slide the fan under the shingles and apply roofing cement as directed. Wire the fan as you would an attic fan.

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