Abstract: A boiler assembly having a unique burner box construction and a modular heat exchanger. The burner box has a primary diffuser upstream from a plurality of burners for evenly distributing a flow of air to and around the burners. The burner box also has a secondary diffuser downstream from the burners for mixing the fuel-air mixture exiting the burners with the air which flowed around the burners to create a final fuel-air mixture which can sustain stable and quiet combustion. The heat exchanger comprises a plurality of sections which define passageways for the combustion gases and circulating fluid. Reticulated ceramic cylinders are located within some of the combustion gas passageways immediately downstream of the burners to enhance heat transfer.

Abstract: An atmospheric reticulated ceramic foam burner which is retrofittable into existing residential heat exchanger designs has been developed to reduce NO.sub.x and CO emissions. It is operated in a blue flame or substantially radiant mode. The ceramic foam tile used is a three dimensional, web-like structure composed of ceramic struts and voids (or pores) which is permeable and rigid and can withstand the high temperatures found in domestic burners. The foam tile is positioned over a manifold, and is the outlet for the manifold. The manifold inlet is a venturi so that incoming gas is mixed with air in the correct range of proportions before passing through the foam. The pressures used, relative to tile porosity, are such that the gas-air mixture does not burn until it has passed all the way through the foam tile, resulting in a flame above the tile. Additional quantities of (secondary) air can be introduced around the burner to mix and burnout the products of combustion.