Abstract: A boiler furnace avoids NOx and increases thermal efficiency with a small boiler. The boiler furnace has a outer water walls and inner water walls. All of the water walls contain water which absorb heat from the flame and cool the water tube which act as a container, passage, evaporator of water and water walls with membrane that connect water tubes to each other. The spaces between outer water walls and inner water walls makes a cylindrical space which contain fires and avoids making a fire that produces nitrogen oxides due to high temperature induced from a concentrated flame.

Abstract: A boiler furnace avoids NOx and increases thermal efficiency with a small boiler. The boiler furnace has an outer water wall and an inner water wall with flared top and bottom portions.