The Thorwaldson Tornado ES-6400 pulls 6,320 CFM with just one motor and it  is priced at $1795 and includes infinitely variable speeds. The only other like it is the QuietCool ES-6400 that must use two motors and blades and has just 4 speeds. It is priced at $1,849.00

You can see it is perfect for hanging from your rafters. It has the damper built in to prevent cold air from falling through in the winter and it has the most powerful 8 bladed propeller ever used in any whole house fan. That is the reason it can move so much air with so little power. Just 505 watts at full speed and when you slow it down the power goes down.


Here are the technical specifications 
Air flow variable from 50 CFM to 6,320 CFM using a dial like a light dimmer. 
Input AC 120 VAC 1 Phase
Input AC power varies from 50 watts to 505 watts maximum at full speed. 
Unit comes in 3 parts 

  1. Main body with motor, blade and damper is 20 inches diameter by 23 inches long. It is suspended from two rafters using the supplied bar and hanger. It has an electrical box with a 6 foot AC input cord and plug plus a terminal for connection of low voltage thermostat wire for the 3 wire speed control. 
  2. Flexible HVAC duct is 20 inches diameter by 8 feet long.
  3. Ceiling mounted flange has 22 inch round white frame under the 20 inch diameter opening in the ceiling that has the 1/2 inch thick  cube core grille. On top is a 20 inch diameter duct collar for connecting the flexible HVAC duct. 

Here is a nice install in Salt Lake City. 


Above is the fan hung from the rafters and to the right is the intake grille and frame.