A CZ crystal growing furnace which has a radiative heat shield that can be raised and lowered above a crucible. The heat shield assembly includes an upper heat shield that is mounted to a furnace cover directly above the crucible. Coupled to the upper shield is a lower heat shield which can move between a first raised position and a second lower position. Attached to the seed holder of the furnace is a bar which maintains the lower heat shield in the first raised position, so that the crucible c...