PURPOSE: To prevent the thermal deterioration of a hot air room heater and to improve the combustion characteristics of the heater by providing a through hole at the bottom of a combustion cylinder and surrounding the outer periphery of the hole by a duct to intake air from a fan from the hole into the cylinder.

CONSTITUTION: Part of air from a fan 14 is fed through a hole 19 into a duct 18. The air is fed via a through hole 16 into a flame port of burner 4 to become combustion air. At this time, the flame 17 is pressed by the air from the hole 16, directed into the inside, thereby preventing it from contacting with the inner wall of the cylinder 15. Part of the air fed into the cylinder 15 is raised along the inner wall of the cylinder 15 to cool the cylinder 15. In addition, when the air before fed into the cylinder 15 passes through a duct 18, it cools the bottom of the cylinder 15 which most feasibly becomes high temperature.