It is better to keep the tub hot, even when you are not using it, unless you won't be using it for an extended period of time. You may think you will save a lot of energy if you let it cool down, but you will spend hours heating it up again, eating up those potential savings of letting the water cool down, It is best to keep the hot tub at a steady cool temperature within a few degrees of what you like to use it at, we recommend around 30 degrees being ideal.