I have an incubator and when I bought it didn't have any way to circulate the air. Everything I looked at moved too much air too fast. I found one of my old computers thrown in the shed and inside it was a CPU cooler fan about 2 inches square. It is 12 volt, so I needed a power pack for a cell phone and spliced the wires together. It works great to keep the whole incubator the same temp and is real quiet too. Cost? nothing.