PSA: I switched from a coal forge to a propane one three years ago and I'm still not sure it was the right call.
I used to swear by the heat control and tradition of coal, but propane is so much cleaner and faster for my small garage setup. The initial cost was about $1200 for a decent two-burner rig. Anyone else made the switch and have strong feelings either way?
Consider the metal itself, not just your shop. I found the reducing atmosphere in a coal fire can change how the steel moves under the hammer compared to a neutral propane flame. It's a subtle thing, but for some complex forging or traditional techniques, that chemistry matters. The clean speed of propane is great, but it might be giving you a different result in the grain of the material. I sometimes miss that dirty, smelly control.
Huh, I remember reading something a while back about how the sulfur in coal can actually change the steel's surface chemistry in a way that helps with forge welding. That's probably part of why it feels different under the hammer. Makes you wonder if we traded a little bit of control for a whole lot of convenience.