Either way, even if you put the probe in the middle of the incubator and you have a fan that produces a lot of heat, it will still be much hotter up top by the fan. I know the fan will push the heat around, but still warmer up top. Heat rises and you have heat being produced by another source other then your heat tape. Hell, I don't know what works and what doesn't, I just read somewhere about a couple breeders that experienced this. Is there a difference in heat generated by a fan between AC and DC?