Abstract: A new control is described for controlling the temperature of hot water or other fluids supplied to rooms of an apartment building or the like, which replaces a prior control. The new control acclimates tenants to the change in temperature resulting from the installation of the new control. The new control includes an acclimating circuit which is used during an acclimating period of a duration such as ten days, which controls the hot water supply system to produce a supply temperature (60, FIG. 2 ) which is between the temperature (46) that would have been supplied by the prior control, and the temperature (44) that will be supplied by the new control after the acclimating period. The acclimating circuit makes the fluid temperature progressively closer to that which would have been set by the new control, at times progressively closer to the end of the acclimating period.