The hot tub is a fickle mistress. Without the right care and maintenance, what is meant to be the epitome of relaxation can become a source of stress. Fortunately, the same basic rules of covering, chemicalization and cleaning apply to hot tubs as they do to pools; that is to say, it's not rocket science.
There’s one critical difference, though: Hot tubs are hot.
The question that stumps many a hot tub owner is that of where to set the hot tub temperature when not in use, especially for extended periods. The general rule of thumb for temperature is that when not in use, the temperature should be set to about 5 degrees lower than when in use. Depending on the climate, this is necessary to keep the water warm enough to reach operating temperature quickly and without wasting energy when the time comes.
However, if you're planning an extended period of non-use (a week or more), it's probably in your best interest from an energy-savings standpoint to lower the temperature further.
Most people make a point of saving energy while on vacation by timing or shutting off lights and climate control systems. The same logic applies to the hot tub. Every day that goes by without unnecessary use of energy is money in your pocket.
Of course, some warmth in the hot tub water must be maintained no matter how long you’re away; no one wants to come home to a miniature hockey rink. Nor is it energy efficient to spend too much time bringing a hot tub’s worth of water up to the desired temperature. Bear in mind that no hot tub is perfectly insulated from the environment and is always losing some amount of heat, hence your pump and heater having to come on periodically.
The bigger the difference between the water temperature and environmental temperature, the faster the heat escapes. This means that during non-use, dialing down the temperature saves energy by virtue of the fact that your heater isn't fighting as much of an uphill battle. While it's true that heating the tub back up consumes energy, a long duration of lower water temperature will more than make up that deficit.
Therefore, for vacations of 7-10 days or more, I recommend lowering the temperature 10 degrees. In most cases, this will allow your system to preserve a bare minimum of heat without uselessly devouring energy. The only catch is that you won’t be able to use the hot tub immediately upon returning.
For the energy savings, though, a few hours spent re-heating the water is probably worth it. Re-heating isn't going to use remotely the same amount of energy as high-temperature maintenance over several days or weeks. On top of that, there's an incidental chemical savings. Chlorine lasts longer at cooler temperatures, so your desired levels will be preserved for longer than normal while the hot tub is "resting."
So, turn the dial down, hit the road, and consider the energy savings a contribution to your mai-tai fund. When you return, there will still be a little piece of paradise waiting for you.