Abstract: In the high pressure furnace disclosed herein, convection currents in the furnace hot zone are minimized by bringing electrical feedthroughs for the heating element through a horizontal spacer ring which separates a pressure body and cover. A heat zone defining chamber base has an annular flange which extends to the pressure vessel body and a hot zone cover has a corresponding flange which extends to the pressure vessel cover. The feedthroughs pass in spaced relation between these flanges. As the feedthroughs enter the hot zone through the space between the flanges, a relatively small volume of unheated atmosphere is available to support convection currents stemming from necessary clearances around the feedthroughs where they enter the hot zone.