They should be set the same, but the water will be at the temperature of the higher setting. In order to have both heaters at the same temperature, the return should go to the first heater so both heaters are being circulated.: In a large home with two 40-gal hot water heaters piped in series, what is best relationship between temperature adjustment of the two heaters? My hot water recirculation line returns to bottom of the final (output) heater. Should it return to the bottom of the first (input) heater?
