The disclosed technology includes systems and methods for operating a pool water heating system. The pool water heating system can include a heat pump, a supplemental heat source, a water temperature sensor, and a controller. The controller can be configured to receive water temperature data and, in response to determining that the temperature of the water is less than a threshold temperature, output a control signal to activate the heat pump. The controller can further determine an expected heating time that can be indicative of an amount of time required for the temperature of the water to be greater than or equal to the threshold temperature. The controller can also generate a heating schedule based at least in part on the expected heat time and a predetermined time of use. The heating schedule can be indicative of a heat pump operation time and a supplemental heat source operation time.

A portable bath tub water heater is provided that includes a water pump and a heating element to heat water in a bath tub, wherein the portable bath tub water heater is configured to recirculate bath tub water using inlet and outlet tubes at least partially submerged in the water. The portable bath tub water heater is configured to be disposed on and/or nearby the bath tub in any number of different ways. After usage, the portable bath tub water heater may be purged of any remaining water and stored for future use.

A portable bath tub water heater is provided that includes a water pump and a heating element to heat water in a bath tub, wherein the portable bath tub water heater is configured to recirculate bath tub water using inlet and outlet tubes at least partially submerged in the water. The portable bath tub water heater is configured to be disposed on and/or nearby the bath tub in any number of different ways. After usage, the portable bath tub water heater may be purged of any remaining water and stored for future use.

The disclosed technology includes systems and methods for operating a pool water heating system. The pool water heating system can include a heat pump, a supplemental heat source, a water temperature sensor, and a controller. The controller can be configured to receive water temperature data and, in response to determining that the temperature of the water is less than a threshold temperature, output a control signal to activate the heat pump. The controller can further determine an expected heating time that can be indicative of an amount of time required for the temperature of the water to be greater than or equal to the threshold temperature. The controller can also generate a heating schedule based at least in part on the expected heat time and a predetermined time of use. The heating schedule can be indicative of a heat pump operation time and a supplemental heat source operation time.

The bathtub device of the present invention includes a water discharge part (8) provided on a bathtub main body, a circulation channel (4), a circulation pump (6) provided on the circulation channel, a temperature modification part (7), a sensing unit (22) for detecting a temperature of hot water in the bathtub main body, and a controller (16) for controlling the temperature of hot water, where the controller performs a water discharge temperature adjustment mode in which the temperature of hot water discharged from the water discharge part is reduced to within the predetermined temperature range, when the temperature is higher than an upper limit temperature of a predetermined temperature range, or a water discharge temperature adjustment mode in which the temperature of hot water is increased to within the predetermined temperature range, when the temperature is lower than a lower limit temperature of the predetermined temperature range.

A bathtub drainage device comprises: a plate, that can open and close an opening formed at a position corresponding to a position where a bather can sit on a floor of a bathtub in which hot water is stored, the plate on which at least buttocks of the bather can be placed; a rising part, that raises the plate closing the opening so that the opening is opened; an acquisition unit, that acquires information indicating a state of the bather; and a control unit, that controls the rising part so as to raise the plate so that the opening is opened and so as to discharge, from the opening, the hot water stored in the bathtub, when the information acquired by the acquisition unit indicates an abnormal state of the bather.