Pit type air circulation furnaces are installed with the opening at ground level or just above it.
These are low temperature furnaces with operating temperatures up to 650°C.

These furnaces are usually used for heat treatment of non-ferrous alloys, tempering of ferrous alloys after hardening, stress relieving after welding and forming, also for ageing.

Since convection is the mode of heat transfer at these temperatures, air circulation is provided inside the retort to maintain stable temperature uniformity.

These furnaces are also suitable for controlled atmosphere based processes.