4" intake flange. Great for small cold frames up to 20' x 96'. Exchanges air in a 100 cu ft room in less than 2 minutes. Flange Type: 3 hole round. (NOTE: We do not currently have any flanges for this blower.) CAUTION: This fan should not be used with a fan speed controller. Voltage 120 Approx. CFM @ 0.0 SP 60 Warranty 1 Year Rated Amperage 0.93 Diameter 4" Rated Wattage 18.6 Frequency 60Hz RPM 3000 Motor HP: 1/80th