For use with Rinnai tankless water heaters (except for models V53e, V53i and R63LSe which must use pressure activation valves) * Temperature setting for connected water heaters is controlled by the temperature controller connected to the water heater with the Master MSB Board. * Includes 1 control board * Allows the customer to connect 2 water heaters * The MSC-B1 must be used with this kit to connect more than 2 water heaters