As far as which forge will consume more fuel when forging a knife, I use less coal than propane. However I have a hand cranked blower so when I'm at the anvil the forge is not using much fuel when the blower is not supplying air. My propane forge runs at full blast when at the anvil using more fuel than needed, unless I reduce the pressure to conserve fuel but that is an aggravation to me. When forging blades, I use coal then switch to propane for heat treating. Does that make any sense? For most general forging I use coal but my wife prefers propane so for us it's an individual choice. That's why I say you really need both.