Muffin fans, pay attention. You pick the "nice" 110 VAC 21W fan from Thermocool, measuring 4-3/4" square x 1-1/2" thick with an unwired offset two-pin power connector, rated for 82-95 cfm and spinning at approx 2600 rpm, with five blades and 3/16" mounting holes at the corners (Mfr part # G12038HA1ST); or the "beastly" 110VAC 36W muffin fan from the same mfr, which blows up to 198 cfm at 2900 rpm and measures 6-3/4" x 6" tall x 2" thick with (2) power terminals on a removable shroud, 5 blades, 5/32" mounting holes on the corners plus a ground lug. Both UL.