QuietCool has a line of whole house fans called Stealth that are not offered on line but must be purchased from a dealer. The average price for the STL PRO-65 installed is $2400. The cost of the unit is not public but is likely to be the same as the QC ES6400 that is priced at $1849.
The STL-6.5 is rated at 6307 CFM and comes with 4 speeds. The unit also includes minimum AC power control and a 4 speed switch. It has a 15 year warranty. It is made up of 2 of the smaller QuietCool units so the installation is more work than the Invisco ES6320.