Abstract: A machine for soldering printed circuit boards and the like includes a housing enclosing an outer process chamber having a soldering station and fluxing station enclosed therein and an inner heating chamber, in combination with input and output transport conveyors on which the circuit boards enter and exit the housing. The heating chamber includes an elevator rack assembly which transports a succession of circuit boards vertically between the input and output conveyors while subjecting the circuit boards to controlled heating. The heating chamber may also be supplied with an inert or reducing gas to facilitate or eliminate fluxing requirements. The environment within the housing is maintained by air lock doors.