I am using a computer blower fan (made for 1U rack units I think) on mine. It does not take a very big fan to provide ample air to hit high temps. Of course, mine is connected to a digital thermostat - I am so lazy when it comes to maintaining temp - set and forget. One issue with a side mounted blower is that I got somewhat uneven burns - I now have a bottom mount and a diffuser and the burns are very even.
Others have used a shop vac to provide air for a burnout. That would practically turn the barrel into a blast furnace.