PURPOSE: To improve operatability and safety, in a petroleum-burning air-warming equipment capable of conducting natural draft combustion by passing of air through a smokestack, by making it possible to continue combustion by natural draft without providing special operating procedure at the time of suspension of power supply or resumption of power supply.

CONSTITUTION: When an adjusting knob 18 of a fuel volume adjuster 16 is turned from 'OFF' position to 'FULL' position, a power source switch 1 is closed, and the current is sent to a combustion blower motor 3 and an ignition heater 4. After ignition, if the combustion unit's temperature rose and a temperature switch 8 was closed, the current is sent to an electromagnetic relay 5, an electromagnetic valve 6 and a convection blower motor 7, and then, combustion is conducted under maximum fuel flow. At this time, if a natural draft switch 10 is turned on, power supplies to the motor 3, the relay 5 and electromagnetic valve 6 are shut off, and the fuel supply becomes minimum regardless of position of the adusting knob 18. Under this condition, the motor 7 is stopped at the time of power failure, and combustion is continuously conducted by the natural draft.