Washer tubes are amazing. I remember the first time a friend brought one to a group camping trip
and I thought it would never generate enough heat to keep 20 people warm. Boy was I surprised.
They are like nuclear reactors melting down and are really efficient on the amount of wood required.
Only problem is finding one that is stainless steel. They are few and far between and it took me over
a year to get mine. You have to want it pretty bad as they usually come with a washing machine attached.
If you can get your hands on an an early 70s washer you probably have one with a stainless tub. Some of the more expensive current front loaders like the Neptune also have stainless tubs.