I use incandescent light bulbs(4x100,200) and an inline thermostat from Bingham's(to 168deg). I also added a small fan inside to circulate the heat. If I want less heat I unscrew light bulb(s). I also have a 1" hole at the top of one end and another at the bottom of the other end that I keep open when drying wood to let the moisture out, by convection. If I am curing glue I plug these holes.