Abstract: An analog computing circuit which controls a boiler or other heating system in a building, has a timer actuated setback which reduces the temperature of the building at night in such a way that as the ambient temperature approaches the lowest temperature in the temperature range for which the heating system is designed, the magnitude of the temperature drop in the building approaches zero. The analog computing circuit includes a timer actuated boost which is timed to start at a fixed time each morning. The boost causes the heating system to supply heat to the building, after the temperature in the building has been reduced the previous night, at a rate sufficient to raise the temperature of the building to its design level by a predetermined time in the morning.

Abstract: Three or more temperature sensors are positioned at various selected locations in a building. These sensors are connected to an averaging circuit whose function is to provide an electrical signal which is functionally related to the average temperature of all these sensors. This electrical signal is compared with another signal which is related to a pre-determined reference temperature for the building. If the electrical signal related to the reference temperature is greater than the electrical signal related to the average temperature indicated by the sensors, a comparator circuit turns a boiler on to heat the building. When the reverse situation is true, the comparator circuit operates to turn the boiler off.