Abstract: A multiple heating/cooling zone control system is disclosed. A heating/cooling system control device continuously monitors heating/cooling zone demand and matches the heating/cooling device output capacity to the total space or heat input required. Within the calculated heating/cooling device output capacity the heating/cooling device is modulated based on zone temperature setpoint to further adjust heating/cooling device output. As heat/cooling loss is increased heating/cooling device capacity and modulation are increased. Should heat/cooling loss decrease heating/cooling device capacity and modulation are decreased. Since heat/cooling output is adjusted based on the heat loss(gain) the heating/cooling device can be immediately adjusted to the proper or matching heating/cooling rate even before water/air temperature based adjustments can be made.