432,613. Heating-plant for buildings. FURLONG, F. A., 2240, Diversey Parkway, Chicago, U.S.A. July 9, 1934, No. 20038. Convention date, July 8, 1933. [Classes 75 (i) and 75 (iii)] The fuel supply in a heating-plant for buildings is shut off when the room temperature roaches a predetermined maximum, and when it drops below a predetermined minimum, successive increments of heat are supplied by turning the fuel supply on and off in accordance with the temperature within the combustion space of the heating plant. In the electrically controlled system employing thermostats shown in Figs. 1, 4 and 5, the heating element of the furnace consists of a heat radiating structure 28 heated internally from gas burners supplied from a fuel-air Venturi mixing conduit 34 fed with gas from a pipe 54 through a valve 46 which is closed by a spring 52 and opened as required by an electric motor 48. A pilot burner 78 is supplied from a pipe 70, 72 which byepasses the valve 46. Air is supplied to the conduit 34 through a hinged flap 66 with an adjustable stop 68 to regulate the supply. In a modification, Fig. 15, the flap is replaced by a plate 366 mounted on bolts with tubular spacers 370 of any required length so as to vary the size of the air opening. To vary the gas supply, interchangeable plates 42, Fig. 3, with holes of various sizes may be fitted in the gas nozzle 46. The opening and closing of the valve 46 is controlled by a thermostat 102, Figs. 1, 4, 5, in the building and a thermostat 82, 84 responsive to the pilot flame and to the temperature of the heat radiating structure 28, the control system being such that the fuel valve 46 is open as long as the temperature of the building is below a certain value, but is cut off when the temperature rises to this point, provided that the heating element 28 has also been heated to a certain extent. The room thermostat 102 consists of a bi-metallic arm 104 engaging two contacts 108, 114, the contact 108 being closed below the minimum temperature such as 70‹ F. and the contact 114 at a maximum temperature such as 72‹ F. The furnace thermostat comprises two bi-metallic elements, the part 82 being in or near the pilot flame and the part 84 being responsive to heat radiated from the heating element 28. The upper end of the thermostat is fixed and the lower end operates, through a rod 88, two tilting mercury switches 94, 96 mounted on a pivot 92. A heat plate 86 directs flame on to the thermostat. When the temperature of the building is below 70‹, the contacts 108, 114 are closed. When the pilot flame is lit, the upper thermostat element 82 bends to the left so as to close the mercury switches 94, 96. A circuit is then completed from the supply transformer 98 through the contacts 108, 114, motor 48 and switch 94 so as to open the fuel valve 46 and thereby close the switch 124, thus completing a second circuit through the switch 96 and contact 114 to the motor. When the heat radiating structure 28 is heated sufficiently by the flame, the heat radiated thereby bends the lower bi-metallic element 84 to the right so as to open switch 96. When the room temperature also rises to 70‹ F., the contact 108 is opened, thus breaking the motor circuit so that the fuel valve 46 is closed by its spring and the switch 124 is opened. Should the room temperature rise to 72‹ F., contact 114 is opened and breaks the circuit through the motor even if the furnace temperature is too low to open switch 96. If the pilot light goes out, both switches 94, 96 arc opened and the fuel valve closes. The wiring diagram of a modification is shown in Fig. 14 and pilot burner details in Fig. 9. The room thermostat 210 closes a simple switch when the temperature falls to 70‹ F. A double bi-metallic thermostat 242, 243 bends in a reverse manner to that of the first construction, to operate a mercury switch 215. When the pilot 232 is lit, the thermostat element 242 bonds to the right and closes the mercury switch 215 against the pull of a light spring 226. If the room temperature is below 70‹, the switch 210 is closed and the circuit through the motor 211, which opens the main fuel valve, is completed. This circuit is opened, either when the room temperature rises to 70‹ F. and the switch 210 is therefore open, or when the temperature of the furnace is sufficient to bend the lower thermostat element 243 to the left and open the mercury switch 215. When the pilot light goes out, the mercury switch 215 is tilted sufficiently by thermostat 242, to close contacts through a circuit 251 which includes an alarm 249. The pilot burner 232, Fig. 9, is supplied from a gas nozzle 231<11> and air openings 231<1>. Secondary air openings 228 are also provided in the tube through which the valve operating rod 225 passes. To light the pilot, a tube 237 opening near the pilot jet is supplied with gas by depressing valve 235 and a switch is then applied to an opening in the tube 237, so that flame travels up the tube.