Abstract: A hearth having an air supply through the bottom, a metal dish arranged at a predetermined height above the bottom and defining an area for preheating combustion air which then flows upwardly around the contour of the dish to form a curtain of preheated air. A belt may be provided surrounding the dish which defines an air inlet slot. The method comprises introducing combustion air into the hearth in the form of a continuous stream to form a continuous ascending air curtain laterally surrounding glowing embers in the hearth. Water or water vapor may be introduced into a zone having a temperauture high enough to decompose the water molecules, thereby locally activating combustion.