Hi Owen: My fresh water holding tank does not have a heat tape. because the tank is next to the Aqua hot, I'm assuming the residual heat from the system is enough to keep the water from freezing. The heat tape is used to keep the waste tanks from freezing. They are not (as far as I know) thermostatically controlled. I believe they are always on and are not HOT but WARM and the heat produced is enough to keep the lines warm enough to not freeze. So basically, it is not like an electric blanket. Why you would have 2 tapes, I have no idea - unless one is wrapped around your black tank and one is around your grey.