|Installing a Whole-House Fan|
|Installing a whole-house fan in an attic floor and using screened attic windows and eaves for venting is a great way to remove excess heat buildup in your home. Depending on the size of the unit and the speed of the fan, air can be completely exchanged throughout a house in a matter of minutes. During hot weather, the fan will keep your house cool until the peak of the afternoon, when the air conditioner can take over. In the winter, it can vent moisture more quickly than passive vents and help prevent the formation of ice dams.
The size of the fan and venting area you need must be calculated on the basis of the volume of space being vented. The airflow drawn in through screened windows and doors from below must be at least equal to the airflow through the ventilation system. The volume of air moved by a fan is measured in cubic feet per minute (CFM) and the fan capacity needed is determined by the cubic volume of your home. A properly sized whole-house fan is capable of changing the air in your home in one to three minutes. The CFM rating of the fan also determines the amount of venting area you will need to prevent air pressure from building up in your attic space. It may be necessary to install additional screened louvered vents in the outer walls of the attic to achieve the required ventilation.
Attic fans come with information on installation and electrical requirements including specific wattage ratings. Some may require power for both a fan motor and a light, and some large fans may require 220 volts. To plan a safe electrical installation, be sure the total circuit demand does not exceed the rating of your fuse or circuit breaker. Installing a whole-house fan is within the range of many do-it-yourselfers but the fan will probably need its own electrical line, and you may want an electrical contractor to install it, especially if it is a 220-volt line, as well as the switch for the fan. When installing the fan use the instructions below as a guide while adhering to the specific instructions that accompany the fan.
Estimated Project Time:
Plan the location of the fan to be where it will be able to draw up air with minimal resistance
Make sure electrical power to the circuit is turned off
Tools and Materials:
Whole-house fan and switch
Screened louver vents, as needed
Scrap pieces of lumber for a work platform, as needed
2x joist lumber
1) Determine Placement of Fan in the Ceiling
Choose a suitable location for your whole-house fan, and mark an outline for the cutout on the ceiling. A hallway or other central location is best. In a two-storied home, locate the fan where it will be able to draw up air from the first floor with minimal interference, for instance at the top of a stairway. Mark an opening in the ceiling below the framing of the attic floor, and cut through the drywall using a drywall saw. Be sure to follow the fan manufacturer's directions when measuring the rough opening required. Wear safety goggles and a dust mask to protect yourself from debris and dust. (Fig. 1) Remove the drywall, exposing the framing joists in the ceiling.
2) Cut the Joist
If your attic does not have a floor, make a work platform by placing scrap pieces of lumber across the joists. Saw through the joist that crosses the fan opening. (Fig. 2)
3) Frame the Opening for the Fan
Set double headers across the cut joist one piece at a time to facilitate nailing and double the full-length side joists if required. Use 2x joist lumber to match the existing framing. (Fig. 3)
4) Install the Fan
With the aid of an assistant, position and mount the fan housing in the opening. Use a circuit tester to confirm that the electrical power is off to that circuit and then make the electrical and motor connections according to the fan manufacturer's instructions. (Fig. 4) Rubber washers or rubber strips between the fan and the framed opening will help to reduce fan vibration and noise.
5) Attach Louver
Working from below, fasten the fan louver into the framed fan opening. On most models, louvers in the cover grille mounted below the fan open automatically when the fan is turned on. (Fig. 5)