The water bay thermostat will turn on the Aqua Hot at approximately 43 degrees F, but only if the diesel burner is on. What I do, when the coach is sitting next to the house, and temps drop, is turn on the furnace heat (the diesel burner) and set it to 45 for the inside of the coach, so it will already be on if the temps in the water bay reach 43 or less. If you have an Aladdin, you can look at outdoor temps and the basement temp on your screen that is for Tank readings. Its at the bottom. I monitor it closely while its in cold weather next to the house before we leave for Florida. Generally...generally, if the inside of the coach is 50 degrees, the basement temp will be the same.