Update 8-17-18 QuietCool is now 4th in the order of highest performance because the company has just complied with the state of California by displaying the true HVI-916 air flow like the other companies do now. But QC still insists on showing a misleading higher CFM value – here is an example from their web site:

Name STL PRO-7.0X Airflow* Hi:6996 CFM HVI-916 Airflow (CA Title 24)** 5200 CFM
The star is “*Listed airflow specs are tested via a device that is calibrated to NIST standards.” which is meaningless because NIST does not have a standard for testing like the HVI-916 has.
So the list below had QC in 2nd place but now shows them 4th.

List shows highest air flow offered.

Thorwaldson   6320 CFM
VentCool          6123 CFM
Airscape           5350 CFM
QuietCool        5300 CFM
CentricAir        3860 CFM
Tamarack         3400 CFM
QA-Deluxe       3396 CFM

Here are all the other suppliers.

Air Vent
Dayton/Grainger
GAF/MasterFlow
Marley
Triangle Engineering
TPI

And in Australia

https://aussiewholehousefans.com.au/
http://www.wholehousefans.com.au/
http://www.Invisco.com.au
http://www.cardiffair.com.au/

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Kurt Shafer YOUR Whole House Fan Guy 800 579 5018