Wood fired baths are an historic tradition, relationship again at minimum to Roman instances when baths known as hypocausts had been built by working sizzling flue gases below a stone tub.  Those Roman tubs have been also off the grid, as are these.  Some are quirky, some passionate, some sensible and some just downright hedonistic.  Which is your favored?
See our other picture essays: Wooden Stoves from Close to the Globe, and and Firewood Assortment and Stacking from about the entire world.