When selecting a whole house ventilation fan system, there are several factors to consider:
1) What size should a whole house fan be for your home? Whole house fans are rated according the cubic feet per minute (CFM) of air that they can move. So the bigger your house, the bigger the fan it will need. If your home has standard 8-foot-high ceilings, just multiply the home's overall square footage by 3 to calculate the right size of fan for the house in CFMs. For example, if your home is 2000 square feet, figure 2000x3=6000. Buy a 6000 CFM fan. If some of your ceilings are higher than 8 feet, buy a slightly larger one.

2)  Fan speed. Look for a two-speed fan. On high, the fan will ventilate quickly; on low, it will produce gentle air circulation. To save energy and reduce noise, you can operate the fan at the lower speed. To cool down the house in a hurry, you can turn it on high.

Why we like it: • 2 Speed wall switch included • Relatively quiet • Automatic shutters open and close

3) Control options. You can have an on/off switch, a multispeed rotary wall switch, a thermostat, or a timer. Timers are recommended over thermostats for whole house fans because timers won’t overcool the house at night. Thermostats could turn the fan on when no one is home (when no windows or doors are open), or when the heating system in the home raises the temperature.

4) Fan blades. The more blades, the better. More blades mean that the fan can move air more quietly. 

5) The fan mounting. The shutters or louvers between the fan and the room should open when the fan goes on and close when the fan turns off and should be designed to seal to prevent drafts and energy loss. (Make sure all the penetrations between the attic and living space are sealed to prevent loss of heated air into the attic during the winter.) Foam strips or rubber mountings help isolate the motor noise from the rooms below. Similarly, a welded frame is less likely to squeak than one that is joined by fasteners.

4) Belt-drive fans are better than direct-drive fans. A direct-drive ceiling fan has its fan blades attached directly to the motor’s shaft for a less expensive but noisier system. Belt-driven units have a motor driving a slower-moving, larger-diameter fan (with four or more blades). This type is much quieter but requires more maintenance because the belts can wear out.

5) Make sure the attic is properly ventilated. Whole-house fans have requirements for minimium attic ventilation. In order for the fan to pull air from the house and push it out through the attic, properly-sized attic vents are needed. Most need 1 square foot of open exhaust area for every 750 CFM. Also be aware that windows and doors in the rooms below will need to be open to provide air for the circulation cycle.