Attic Fan Installation

An attic can get insanely hot during the dog days of summer! You may not realize how much heat is trapped above your head, but it certainly affects your electric bill.

One way to control the amount of heat and humidity collected in your attic is by installing an attic fan. An attic fan works just like the exhaust fan in your bathroom but on a larger scale. It’s a bigger, more powerful fan that can cool your entire house substantially without using much energy.

A properly installed attic fan expels hot air through a gable or roof vent while cooler air replaces it through soffit or other gable vents. An attached thermostat can automatically cycle the fan on and off, depending on the temperature in the attic. There are solar-powered fans with photovoltaic panels that power everything and require no wiring at all that can potentially save you even more.

Installing an attic fan sounds harder than it actually is. If you follow these steps in the spring, this summer, your house will be more comfortable. What's more, your energy bills will be lower than ever.

Step 1 - Pick the Location

Determine where you’re going to get an electrical feed for the exhaust fan. In most cases, it’s easiest to branch off the attic’s light fixture.

Step 2 - Put on Your Protective Gear

Wear a long-sleeved shirt and long pants to help protect your skin from the itchy insulation, and also goggles and a face mask to protect you from breathing it in or getting it in your eyes.

Step 3 - Prepare the Opening

You may have to replace the existing vent when you install an attic fan. Use the provided template to trace the new opening onto the wall. If you didn't get a template, trace a smaller layout by 5/8 inch. That will allow enough space to attach the cover while overlapping over the opening.

Step 4 - Cut a Hole and Make the Frame

Use a saber saw to cut out the new hole for the fan. Install the louvered cover by screwing it in place and then seal the outside of it with acrylic caulk. Next, cut two pieces of 2x4 to fit between the studs on either side of the louvered cover. Nail them in place, one above and one below the cover, creating a frame to mount the fan.

Get a piece of plywood large enough to cover the newly framed vent opening. Measure and cut the plywood so that it can easily be mounted to the frame. In many exhaust fan kits, a traceable template of the fan is included. Place the template (or the fan itself if the kit didn’t come with one) directly centered on the plywood. Trace around the perimeter. Use the saber saw to cut out the opening.

Step 5 - Install the Fan

Center the fan over the opening and screw the housing to the plywood. Give the blades a spin to make sure they turn without hitting any obstacles. When installing the plywood, be sure to note which part of the fan is supposed to be on the top side—this will be marked on the housing. Hold the mounted fan up against the frame and screw it into the studs, one screw in each corner. Then, check to make sure it is level. Once it is, add a few screws to each side, so it’s held down tight.

Step 6 - Mount the Thermostat

The thermostat should come in a metal box that can easily be mounted to the plywood. Remove the cover and the controller. Place the back of the thermostat box at one of the lower corners of the plywood, level it, and screw it in place. If the fan doesn’t already have metal sheathing covering its wires, you will need to buy some. The metal sheath gets connected to both the fan and the thermostat's junction box with metal conduit connectors.

Step 7 - Run the Electrical

Now that the fan and the thermostat are both mounted on the plywood, and the plywood is mounted onto the frame, it’s time to run the electrical. Of course, if you went with the solar-powered fan, you can skip this. This next step is to determine where the power line will come from—from the light socket or the light switch. It is quite easy to determine which just by looking at the light's junction box.

If two cables lead to the light fixture, one of them comes directly from the power source while the other returns to the light switch that operates it. You can hook up the line from the fan in that junction box. However, with only one cable going to the light fixture, there will be no power there when the light is switched off. You'll then have to hook up the fan ahead of the light switch.

With an alternate light source set up, switch off the circuit breaker to avoid any risk of getting an electric shock. Knowing now which of the junction box houses the 120 volts source, open it up and remove a knock-out from the box. Strip away about eight inches of the sheath from the Romex from the fan and secure the cable through the knock-out opening with a cable connector. After removing 3/4-inch of the insulation from the white and black wires.

7.1 - From the Light Switch

Remove the black wire from the switch's terminal (the hot wire) and replace it with a short piece of black wire, with 3/4-inch of the insulation removed from both ends. Connect the three black wires, then connect all the white wire, and finally the ground wire to the box before closing it up. Use wire nuts for multi-wires connections.

7.2 - From the Light Fixture

You'll likely see two white wires connected to both socket terminals. Remove the white wire from the socket's threaded tube (outside terminal) and replace it with a piece of six inches long white wire with 3/4-inch of the insulation removed from both ends. Connect the other end of it, the white wire from the fan cable and the neutral (white) from the power cable. You can now connect the three black wires together and the ground wire to the box. Use wire nuts for all multi-wires connections.

At the thermostat, strip 3/4-inch of the insulation from each of the incoming wires and connect all the white wires with a wire nut. Connect all the ground wires and secure them to the grounding screw inside the box. The black wire (hot) coming from the light or the switch gets connected to the black wire on the thermostat, while the black from the motor gets connected to the red wire from the thermostat. Secure all the wire connections with wire nuts. The thermostat can now be closed up and set to 95 degrees.

Back at the light fixture, Reinstall the light fixture and turn on the breaker.