A vapor furnace producing stable atomic and molecular beams for photoionization experiments is described. During operation the furnace causes no detectable magnetic stray field because it is heated by a stream of hot air. Thus angle‐ and energy‐resolved measurements of photoelectron spin polarization could be done at a kinetic energy as low as 0.5 eV. The high temporal stability of the target beam is demonstrated by means of an angular distribution measurement with mercury atoms.