The copper coil without a pump would take days. With a shurflow 2088 pump and a good consistent fire the coil will heat a 6 to 8 person tub in about 12 to 15 hours. I know I have done tons of these.
this is all about ease and speed. Camping in the rain or snow it's more about the booze and fire and a tub at the river with wifey.