The heated furnace acts like a regular furnace but doesn't burn coal to smelt things, heat must be applied externally to the block using coils.
Another easy GUI: input on the left, output on the right.
Automating the Heated Furnace
All sides can be used for both input and output but the furnace does not auto eject smelted items (unless you install the upgrade).
There is only one upgrade that can currently be applied to the Heated Furnace: the auto-eject upgrade. When this upgrade is installed smelted items will be pushed out automatically by the furnace, it will first try to output to pipes, then to inventories.
The side output priority and if it should output on a specific side can be configured with the Machine Configurator.