Abstract: A portable water heating system for use with a spa. The heating system circulates water from a spa, heats the water and returns the heated water to the spa. The portable heating system includes a housing that encloses a heater and a pump; a water intake hose; a water outlet hose; and a thermostat. The heating system may also include temperature-setting dials and flow and pressure regulating switches. A thermostat is also disposed within the portable spa heating system and is attached to the heater. The thermostat may be set to a predetermined temperature so that the heater, and therefore water temperature, may be controlled.