Every hot tub breaks down into two components: the shell and the cabinet. The shell is the weather-resistant outside. Just below the shell, the tub is supported by foam or fiberglass. The hot water is generated in the cabinet, which is made of polymer or wood. It stores the system of tubes, heaters and pumps. Some hot tubs have tanks to store hot water. More common are tankless hot tubs, which are more efficient and supply more hot water.
Electrical Resistance Heaters
Hot tubs are warmed by electrical resistance heaters. Water courses through the assembly housing, where it comes into contact with an element coil that generates heat. The outside two layers of the assembly housing are the outer sheath (which is often gray) and the compacted filler and insulator.
Heating the Water
One or more pressure pumps send the water through the heater, which is usually located in the cabinet. The water is sent through the assembly, where it comes into contact with the heating coil, which wraps around the cold pin. The heater converts energy from the terminal into heat for the water. If the coil heats for long without water, a "dry fire" might occur. A "dry fire" happens when the heating coil overheats because the water is not absorbing the heat as it should. Damage to the hot tub may result.
Jetting the Water
After being heated, the water runs to a distribution box, which branches out to the various jet nozzles that lead into the tub itself. The "jet effect" is caused by forcing a significant amount of water through smaller nozzles. The water is continuously heated by the heating system in the tub.