Abstract: Method and device for firing solid fuels, substantially in the form of lumps or pieces, in a furnace having a combustion chamber (1) with a sustantially horizontal bottom (10), upon which is maintained a fuel bed (3) with relatively great thickness while supplying fuel within the very bed (3), through which bed primary combustion air is fed from below through mutually spaced primary air passages (18) in the combustion chamber bottom (10), the combustion gas which leaves said chamber (1) furthermore being subjected to a subsequent secondary combustion in a secondary combustion chamber after addition of secondary combustion air.