The Sellers gas fired steam boiler is a horizontal single pass packages unit of a uniquely simple design. Instead of having a single large combustion chamber, the gas is burned inside many small tubes. These ” immersion fired” tubes are widely dispersed and totally submerged in the water. As a result, thermal stresses are greatly reduced. The boiler is completely water-backed and requires no refractory or brickwork.
Each of the firing tubes operates in an identical manner. The premix burner delivers the same amount of gas to each tube. This causes each tube to operate the the same temperature eliminating “hot or cold” passes. Combustion takes place and is completed in the forward half of each firing tube. Fifty percent of each tube provides primary heating surface upon which the fire shines. It is the quantity of primary heating surface in a boiler that determines the metal temperature in the zone of combustion, the hottest part of a boiler. Sellers large primary heating surface area keeps tube metal temperatures low. This reduces metal stresses and provides long equipment life.