This is one of the most important factors to consider when looking to buy a hot tub. Different hot tubs cost different amounts of electricity or gas to run them. Built in swimming pool style hot tubs are more often than not plumbed to a gas heater. These hot tubs rarely have insulative covers on them and therefore cost quite a bit to heat them up. One of my best friends only uses his swimming pool hot tub twice a month because it costs too much to use more often than that. An extremely important factor in choosing an energy efficient hot tub is the insulation used. Hot Spring spas have fully insulated cabinets that keep them the heat in the water rather than allowing it to cool and escape. The thick insulative cover also keeps the heat in and reduces the energy used to heat the water. Bigger and more powerful jet pumps are not a good thing in a hot tub if energy use is important to you. Hot Spring spas designs and engineers each model to have appropriately sized pumps and heaters to efficiently heat the water and give a strong hydrotherapy massage. There are many hot tubs that do not properly engineer their jet pumps for the size of the hot tub and therefore cost much more money to run. Many of these hot tubs are also not fully insulated or rely on the warm air in an empty cabinet cavity or a thin space blanket for insulation. This minimal insulation causes the hot tub to cool more quickly and in turn run the jet pumps to circulate water through the heating system. These less insulated models with large jet pumps will cost much more to keep hot than a fully insulated and properly sized pump system in a Hot Spring spa. Depending on the size of the model you choose, you can expect a Hot Spring spa to add between $15 and $50 per month to have your hot tub hot and ready all the time. This can be slightly more or less depending on the kilowatt hour rate you pay your utility company in your area. Rest assured that your Hot Spring spa will be extremely energy efficient.