I talked with Bob at Pro Heat and I understood what his logic was with the probe being on the cool side. The snake will regulate itself from the hot side to the cool side as needed. But what shocked me more was when he asked what thermostat I was using, told him a Herpstat 2. He said that he does not recommend those because they are not UL listed, and that the best on market is the Hydrofarm thermostat. Seems strange.......