Installing a Whole-house Ventilating Fan

Intro

A whole-house fan pulls fresh air through every room that has an open door or window and sends it out through the attic.

The attic must be vented and doors or windows must be open in the rooms below. Locate the fan in the ceiling of a top-floor hallway. The fan can rest on top of an exposed joist or frame an opening.

In winter, make sure the fan's shutters close tightly, and place insulation over the fan so the house won't lose heat.

Checklist

Time
About 8 hours to run cable and install a fan with a wall switch (not including preparing a path for the cable)

Tools
Voltage tester, stud finder, tape measure, drywall saw, drill, circular saw, hammer, fish tape, nonconductive ladder, screwdriver, long-nose pliers, lineman's pliers, strippers

Skills
Splicing and connecting wires to terminals, installing boxes, running cable through walls and ceilings, cutting and attaching boards

Prep
Find a power source and make sure the fan does not overload the circuit. Spread a drop cloth on the floor. Enlist a helper for lifting and placing the fan.

Materials
Whole-house fan, remodel box, switch, electrical boxes with clamps, three-wire cable, wire nuts, electrician's tape

Cut through the ceiling board and pull back insulation to create a channel for air from the house. Mount the fan on top of ceiling joists. The fan draws air from the house and pushes it out through gable, roof, and eaves vents.

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Select Size and Capacity

To properly cool a house, the fan should exchange the air in a house at least once every four minutes. The faster the air exchanges, the cooler the house.

Manufacturers offer several sizes of whole-house fans. Determine the total square footage of your home and consult with a salesperson or read the manufacturer's literature to choose the right size for your house. When in doubt buy the next size up; with a fan-rated multispeed switch, you can always adjust the power downward.

Step 1

Cut a hole for the switch box into a wall below the fan. Run three-wire cable down through the ceiling plate to the hole.

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Step 2

Position the fan so it rests on joists at either side; one joist runs through the middle. Use a stud finder to find the center joist, then cut a locator hole and measure to find the exact location of the joists.

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Step 3

Cut the hole according to manufacturer's directions. Lay pieces of plywood on the attic joists to provide a safe work surface. Work with a helper in the attic to lift the fan into place.

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Step 4

Remove insulation that's in the way. If the fan does not come with blocking to fill gaps between the joists, cut blocking from lumber the same dimension as your joists. Build a frame of 2X4s, lay it flat and squarely on the joists, and fasten it firmly.

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Step 5

Center the fan over the frame. Attach it by driving wood screws (not drywall screws) through the brackets provided and into the frame.

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Step 6

Shut off power to the circuit you are using. If there is a junction box in the attic and its circuit can accommodate the fan, pull power from it. If several cables enter the box, use a voltage detector to make sure all power is off.

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What If No Power Is Available in the Attic?

If there is no usable power source in the attic, run power up through a wall switch and then to the fan. Check that adding the fan to a nearby fixture or receptacle circuit does not create an overload. Shut off power to the circuit and tap into the power source. Then run cable and install a switch box. If using a fan-rated speed control, wire it as shown.

Step 7

Remove knockout slugs and run two three-wire cables, one from the fan and one from the switch. If the fan has a cable whip that does not reach the junction box, run it to an intermediate box and run cable from there to the junction box.

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Junction Box and Switch Wiring

The hot wire in a junction box is usually a black or colored wire that is spliced with other black or colored wires. This diagram shows how to wire a two-speed switch.

Step 8

In the junction box, connect the grounds and splice all white wires in the box, except the one running to the switch. Mark it with black tape and splice it to the black wire running to the fan. Splice together the other black wires and splice the red wires.

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Step 9

At the switch hole, clamp cable to a remodel box and install the box. For the two-speed switch shown above (provided by the fan manufacturer), mark the white wire with black tape and connect it to the black switch lead. Splice the red wire to the red lead and the blue lead to the black wire.

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Step 10

Check the fan belt tension. When pressed it should deflect about 1/8 inch. If necessary follow the manufacturer's instructions for adjusting the tension. (Not all whole-house fans are belt-driven; some have blades powered directly by the motor.)

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Step 11

With a helper position the shutter so it covers the ceiling hole. Drive screws into joists to attach the shutter firmly to the ceiling. Restore power and test. Be sure the shutter freely opens and closes.

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