The first and most important recommendation is that your hot tub cover is in good shape. Because heat rises, a well insulated, well working cover will help keep the heat from escaping. When not in use, the cover should be securely strapped down to the side of the hot tub.
If the cover is old or worn, a replacement, though expensive, is necessary and will save money in the long run. Additionally, Spadepot recommends the use of a windbreak, which will not only add privacy and attractiveness, but "can also significantly reduce heat loss."
Modern spas come with a default temperature setting of 104°F. By turning this temperature down to 102°, money can be saved on your energy bill, as it takes considerably more power to heat the water an extra couple of degrees. When you go on vacation, turn your hot tub heater to the lowest possible setting or completely off. Off-peak heating, or heating your tub when power is lowest in demand, is another way to save money, as some power companies reduce their energy costs during this time.
To save even more on your hot tub energy bill, turn off the lights, jets and air blowers. Not only is energy being used to blow air through the jets, but this air also decreases the spa's temperature. Moreover, clean, unclogged filters will allow the water to circulate, thus allowing the water to heat more efficiently.