Imagine having different types of furnaces/upgrade for the firepit: a stone one for cooking food, and a brick one that melts ore faster than the classic firepit. It could look like a Bloomery, but with an opening and not be single-use.
It would be better than just using the same firepit for cooking and smelting throughout the entire game.
It could work as an upgrade to the firepit, evolving through the different ages and interacting with the new bellows introduced in version 1.22.
For example, at the start it could simply be stones placed around a fire. In the Copper Age, it could be made with clay and loose stones. Later, it could be built with bricks, and eventually evolve into a small cast iron stove used only for cooking food.
Thank you for your incredible work and for reading my suggestion. Keep it up!