The fan underneath the printer is left over from a MakerBot Rep 1 attempt at a patch for an overloaded voltage regulator., and the fan didn't fix it. The original open source plans still had the fan and that is what the Chinese copied. There is no reason for the fan underneath the printer, and I have had one hooked up in over a year, on either printer. The stepper drivers the fan blows on run at about 20% of their rated capability so they are practically idling.