Slag-free discharge of molten metal from a smelting furnace is assured either through slow tilting through a small angular range in case the outlet is located in a lateral bay extension of the furnace such that maximum depth level is retained above the outlet and the furnace is tilted back to a slight negative angle once the formation of eddys that could suck slag into the outlet becomes likely. In the case of a central discharge outlet, maximum depth level is still maintained above the outlet but the slag is stiffened, i.e. rendered highly viscous, so that any eddy will not tear slag particles off and suck it into the outlet. Certain ratios of water cooled surfaces to fire proof surfaces are to be observed.