In-line heater and ozonater interlock to operate when the pump is in operation. This is a 1.5 KW, 12 volts, 12.5 A heater which requires a dedicated GFCI circuit. The heater maintains the water temperature and the Ozonator provides an additional level of sanitation. Devices that claim to produce heat keeping the bathwater hot by friction have no scientific testing to verify that false claim. Click here for more info.