A few people on here say they use no fan at all. Their is a story about the Perana where Basil Green leant down noticing the fan and setup was blowing the air in the wrong direction and had to redesign it. As has been stated that a 14 inch will blow so much more than a 12 inch when it comes to air flow. Also the blade design and number of blades makes even more difference so spending money on a good quality thermo fan is essential.