Get to know the hot tub equipment and how it operates. Not all hot tubs have the exact same equipment, but they all have these items in common: a filter, pump, heater and jets.
The purpose of a filter is to keep the water clean. As water flows through the filter it traps oils, dirt, hair and other organics in the water. The hot tub will contain either a skimmer/filter combination near the water line or it will have what is called a pressure filter, which is a cartridge canister located in-line with the other plumbing located after the pump. For larger built-in hot tubs you also have the option of using a DE (diatomaceous earth) or sand filter.
The pump is what circulates the water in the hot tub. Most portable hot tubs will come equipped with the appropriate size pump for that particular hot tub, but if you are looking to create your own built-in hot tub, you should choose a pump capacity that fits the water volume of your hot tub. Also, keep in mind the more jets your hot tub has, the more horsepower that is needed. Some hot tubs contain more than one pump or have pumps with a two-speed design.
The hot tub water is warmed as it passes through the heater assembly. Heaters to choose from are either electric, gas, propane, oil or solar powered. The climate in your area, the size of your hot tub, and the voltage of the heater all play a big part in its ability to heat the water up quickly. The amount of insulation around the hot tub will determine its ability to maintain that heat. A professional hot tub dealer/builder will be able to help determine which heater is right for you.
Water returns into the hot tub through jets, which give you a burst of water that creates a soothing massage. The water rushing through the jets is powered by the pump, so make sure you have the correct pump size to fit your hot tub. Many hot tubs have a feature that allows a mixture of air and water to flow through the jets by way of an air venturi system or a blower.