Visit http://www.gopoolandspa.com/hot-tub-heaters.html now! In order to get your hot tub water nice and warm, it needs to have complete working hot tub heaters. In a hot tub, the water travels through an assembly housing unit where it connects with an element heating coil that gives off heat. The pumps send the water to the heater where the coil in the heater heats it up and sends it back into the hot tub body through the jets.