Abstract: A core box has a thick walled cope and a thin walled metal drag mating in essentially a horizontal parting plane. The cope and drag each have ports therethrough screened to prevent passage of sand, the ports communicating with the interior of the core box. Resilient seals seal and reseal the cope and drag at the parting plane. A convection heater delivers a heated gas, to drag ports and thence out through the ports of the cope, the convection heater having a heat conductive manifold attached to and along the drag for augmenting the heat of the gas as it passes to the ports of the drag. Conduction heater (burner units) directly heats both the cope and manifold and thereby the interior of the core box by conduction. The convection heater heats the gas in two stages, first to a temperature level outside the core box and manifold and thence to a second temperature level elevated by exposure to the manifold. The temperature levels are respectively about 175.degree.-225.degree. F. and 250.degree.-290.degree. F.