The most common type of hot tub is the electric model, which uses a heater powered by electricity. These are generally easy to install and use, but they can be costly, depending on the price of electricity in the region in which the tub will be installed. A gas hot tub is much less expensive to operate, though the initial installation cost will generally be much higher than that of an electric model. In some cases, it may be necessary to run a gas line to the tub, which means the gas hot tub installation can be even more expensive.
Gas is run through a pipe to a specially designed heater that will accept the gas line. Once the gas reaches the enclosed heater, it will be lit or combusted to provide heat. The flames will shoot through a heating element that will in turn heat a water tank. The water from the tank will then be fed into the tub itself, providing hot water to the gas hot tub. The larger the burner, the more heat can be produced. Not all systems are as efficient as others, and many factors will affect how well the water temperature can be regulated, how quickly the water can be heated, and how much gas will be required to heat the water.
A water circulation system is used as part of the gas hot tub system as well. This system allows the water from the tub itself to be pumped into the water tank so it can be heated. Once the water has been heated sufficiently, it can be returned to the tub through another pipe. This continual movement of water ensures the tub stays at a consistent temperature for a longer period of time. A user will end up consuming a fair amount of gas in the long run, but the cost of gas is usually much lower than the cost of electricity, meaning a gas hot tub will be far less expensive to operate.
Sometimes a gas hot tub is designed to be more portable; if this is the case, an external gas tank that is removable and usually fairly small can be used to power the gas system. The tank will usually be limited in its ability to warm the tub for a long period of time, however, and will need to be replaced once the gas runs out.