A thermostatic modulation control valve plumbs in line with a boilers gas valve and functions to automatically adjust the boiler output rate (or modulate the size of the flame) according to the current heating load. Thermostatic modulation valves made by Honeywell come in several different models which operate within different BTU output and temperature ranges. These valves are ideal for multi-zone systems that have single stage gas controls. Because of these valves, better system energy management can be obtained from a boilers single stage gas system that cannot by itself take full advantage of a systems multi-zone design. Without the valve, whether one zone or three zones are calling for heat, the boiler is firing at full capacity, even if the heat load of the structure is not requiring full input. The boiler fires full anyway, short cycles because of too much power and efficiency is lost. A boiler burning under load is more efficent than a boiler shutting on and off constantly. So when one or two zones are calling for heat, and a modulation valve is used, the boiler may only be burning at only 40%-70% of capacity. Modulation valves, in turn, also allow a boiler to operate longer within the system design temperature range by reducing the fire rate as the boiler nears its desired temperature setting. This will further increase the efficiency of the heating system and, therefore, can lend its application well even to single zoned systems too.