The invention relates to a method for intensifying the burning of solid fuels in fireplaces, in which fuel is heated up and gasified in a fire chamber (8). Furthermore, the invention relates to a device for applying the method, which device includes a fire chamber (8). According to the method in the burning of fuel, the burning of gases in it is separated from the burning of solid carbon in the fuel by releasing gases from the fuel in the fire chamber by means of heat and by conveying them to a uniform, planar flow of combustion air in the top part of the fire chamber in which air is conveyed and in which gases are burned. In the device according to the invention, on the edges of the top part of the fire chamber there is all around a gap (3, 13, 23) entering from a combustion air channel/channels which is directed towards an exit opening (4, 15, 25) along the bottom surface (14, 24) of the top part of the fire chamber advantageously in the middle section, from which a flow channel extends to an afterburner (31) being above it, the inner surface of the fire chamber is of heat-resistant material having a low heat capacity, behind it there is a heat insulator layer (18), and in a batch-burning fire chamber there is in the bottom part a grate (7, 17) or inside the grate a char basket and an adjustable supply mechanism of combustion air.