Abstract: A heating boiler comprises separate furnaces for oil and solid fuel. The oil combustion chamber can be connected directly to flues in contact with water via an afterburning chamber (11) common to the two furnaces. The connection (22) between the oil-combustion chamber (8) and the afterburner chamber can be shut off by a damper (25). Instead a connection is opened between the oil combustion chamber and the furnace (9) for solid fuel via an ash compartment and a grate (20) under the furnace for solid fuel. Through the arrangement with the damper (25) a number of possible variations can be obtained depending on the actual heat requirements.