Abstract: A boiler for combustion of solid fuel, especially biomass, a first combustion stage with a primary air supply, an igniter, a fuel supply, a second combustion stage a burn-up and calcination space, a combustion chamber which is upwardly open and with a flue, the burn-up and calcination space being located underneath the combustion site such that fuel can be moved from the combustion site of the first combustion stage into the burn-up and calcination space. The primary air supply is located within the combustion chamber above the combustion site such that air can be blown into the first combustion stage, flue gases which form in the burn-up and calcination space are routed essentially passed the primary air supply means and the combustion site so that the flue gases of the second combustion stage do not adversely affect the combustion of the fuel at the combustion site.

Abstract: A boiler for combustion of solid fuel, especially biomass, a first combustion stage with a primary air supply, an igniter, a fuel supply, a second combustion stage a burn-up and calcination space, a combustion chamber which is upwardly open and with a flue, the burn-up and calcination space being located underneath the combustion site such that fuel can be moved from the combustion site of the first combustion stage into the burn-up and calcination space. The primary air supply is located within the combustion chamber above the combustion site such that air can be blown into the first combustion stage, flue gases which form in the burn-up and calcination space are routed essentially passed the primary air supply means and the combustion site so that the flue gases of the second combustion stage do not adversely affect the combustion of the fuel at the combustion site.