A method of controlling a steam heating system on a zone by zone, and radiator by radiator basis, through the electromechanically controlled release of air from radiators. A programmable set of target temperatures for each zone is stored in a microprocessor module. The microprocessor monitors the air temperature of each zone through probes. The microprocessor can selectively open and close the electromechanical air vent valves installed on each radiator's vent port. When one of the vent valves is caused to be opened, the steam boiler is triggered to start producing steam pressure; steam displaces the air in the radiators, out the vent valves, heating them up. Each zone's temperature is achieved and maintained by controlling the associated radiators' output through modulating their air vent valves. Through the microprocessor's adjustment of the vent valves' temperatures and cycle timing, optimal energy efficiency across multiple zone control is achieved.