A melter apparatus includes a floor, a ceiling, and a substantially vertical wall connecting the floor and ceiling at a perimeter of the floor and ceiling, a melting zone being defined by the floor, ceiling and wall, the melting zone having a feed inlet and a molten glass outlet positioned at opposing ends of the melting zone. The melting zone includes an expanding zone beginning at the inlet and extending to an intermediate location relative to the opposing ends, and a narrowing zone extending from the intermediate location to the outlet. One or more burners, at least some of which are positioned to direct combustion products into the melting zone under a level of molten glass in the zone, are also provided.