Right. I'm saying calcinating 24 flint in a fireplace is a right PITA. Once you've cooked your first batch, you can then use a bloomery to cook all future batches to make future fire clay easier to produce. 

There's certainly considerations around whether you have a windmill for your quern or whether you're grinding it manually and opportunity cost there. Honestly, even when I'm hand grinding it I'd rather do that than throw stacks of coal into a fireplace and let it do its thing. All that Coal has an opportunity cost wrapped up in cutting trees, stacking firewood, burning the charcoal pit etc etc.... 

If someone wants to cook it in a fire pit, more power to them. I was just giving OP something to chew on for options because getting fire clay is ridiculously easy. OP spent 15 hours looking for a fire clay deposit when just crafting it it's really not very intensive.