Abstract: An insulated firebox is disclosed which forms a portion of the combustion chamber of a pool heater and which is adapted for reducing the emission of smoke and odor from the firebox into the atmosphere. The firebox is comprised of insulation material which defines a combustion chamber enclosed by the insulation on its vertical sides. The insulation contains organic materials capable of resulting in the generation of smoke or odor. A liner extends substantially continuously about the insulation and seals the vertical sides of the combustion chamber from the escape therethrough of the organic materials contained by the insulation. The organic materials are thus directed into the combustion chamber, where the higher temperature will result in more complete combustion of the materials with a consequent reduction or elimination of the potential smoke or odor.