Attic Fan Installation
| An attic should be ventilated year-round.
In summer, ventilation prevents excessive heat buildup, which
may shorten the life of some roofing materials and drive up
cooling costs. In winter, ventilation pulls out interior
moisture, which tends to collect in attics and may saturate
insulation or cause mold and mildew to grow. In general, you
should provide vents equal to 1/300 of the ceiling area of the
top floor. For truly effective cross-ventilation, vents should
be located low (as soffit grilles or continuous soffit vents
at the roof eaves) and high (near the roof peak, in the form
of either gable-wall vents or fans, ridge vents, or roof
ventilators). |
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This project describes the basic steps to
install a powered ventilator in a gable-end wall. Choose a model
that is controlled with a thermostat and, if moisture buildup has
been a problem, with a humidistat.
1. Determine Fan Capacity (Attic Fan
Installation): The
Home Ventilating Institute recommends that one or more power attic
ventilators provide at least 10 air exchanges an hour. Multiply
the length by the width of your attic floor to determine its area,
and multiply the result by 0.7 to determine how many cubic feet
per minute (CFM) of air the fan(s) must move.
(L x W) x 0.7 = CFM
Add 15 to 20 percent to the result for
steep roof pitches (such as 8/12 pitch, which means 8 inches of
vertical rise in 12 inches of horizontal run) or if you have dark
roof shingles.
2. Determine Intake Vent Requirements
(Attic Fan Installation):
Divide the CFM capacity of the fan by 300 and multiply by 144 to
determine the minimum area (in square inches) of intake vents.
(CFM / 300) x 144 = min. area (sq.
in.)
For information on soffit vents contact
The Home Ventilating Institute (a division of the Air Movement and
Control Association International Inc.) at 847-394-0150.
3. Cut Wall Opening (Attic Fan Installation): Working from the top down, remove the
siding below the roof peak and center and level the template for
the louvered vent, as shown. Following the manufacturer's
instructions, bore a starter hole through the wall sheathing and
cut the opening with a portable jigsaw or reciprocating saw. (If
you have an adequately sized louvered vent, skip to Step 6.)
4. Frame the Opening (Attic Fan Installation): Provide framing and/or a plywood
mounting board, as directed by the manufacturer. Additional
cutting of existing framing from the inside may be required.
- Caution (Attic Fan
Installation): Provide adequate
work lighting. Lay down a temporary floor, such as a piece of
plywood, if needed. Wear goggles and dust mask.
5. Install the Louver or Shutter (Attic Fan Installation): Secure the exterior
accessory shutter (shown) with screws and reinstall the siding.
Siding manufacturers are usually good sources for how-to
information on siding installation and repair, which vary
according to the type of siding.
6. Mount the Fan (Attic Fan Installation): Mount the fan to the framing or mounting
board with screws, as directed by the manufacturer.
7. Install the Controller (Attic Fan Installation): Remove any knobs and the cover
so you can secure the controller to the mounting plate or studs
with screws, and follow the manufacturer's instructions for
locating the unit. Do not substitute controls (such as solid-state
speed controls) that are not approved by the manufacturer.
8. Make Wiring Connections (Attic Fan Installation): All electrical work must be
done in accordance with local codes. If you are not familiar with
basic wiring procedures, hire a licensed electrician. Follow the
manufacturer's wiring diagram to make the connection to your power
supply. Shut off the breaker or remove the fuse for the fan
circuit; and verify that it is off using a neon circuit tester.
9. Adjust Settings (Attic Fan
Installation): Thermostats
and humidistats are adjustable. Follow the manufacturer's
guidelines and instructions to make the necessary adjustments.
 
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