To lower the running cost by always maintaining stable warmth keeping state regardless of the outside air temperature and installation environment in bath hot water supply equipment, and efficiently performing warmth keeping operation.
This automatic bath warmth keeping device 30 includes: a means 23 for setting the warmth keeping temperature of a bath; a bath heat exchanger 9 for heating the circulating bath water; a circulation pump 12 for circulating bath water; a temperature sensor 13 for detecting hot water temperature in the bath; and a control part 2 for detecting the bath temperature after the lapse of a preset interval time, and giving an instruction for starting the operation for reheating of bathtub water when the detected bath temperature reaches a preset bathtub water reheating operation start temperature or less, and continuing the operation for reheating of bathtub water until it reaches the bathtub water reheating operation end temperature. The control part estimates the time elapsed until the operation for reheating of bathtub water starts by linearly interpolating a change in bath temperature measured at two different points of time in the bath temperature detecting interval time ts, and sets the estimated time as the next bath temperature detecting interval time ts.
SUGIYAMA KAZUICHI
TAKAGI JUNICHI
