I measure how much air a fan pushes out a window by measuring the speed of the air entering the room.  Lowe's said the Lasko 3733 would blow 2500 cfm for 80 watts.  I bought it to replace a five-blade Holmes box fan that exhausts 800 cfm for 135 watts.  I found that the Lasko exhausts only 800 cfm for 90 watts.