I’ve also seen these marketed as “Cowboy” hot tubs, but the principle is the same. They are powered by an external wood fire that heats coils connected to the tub. The difference in temperature then causes convection to circulate the water, bringing cool water in for heating and hot water out into the tub. While slow, they are quiet, lack many parts (moving or otherwise) to service and can be used “off the grid”. I suppose you could also make epic amounts of soup.
Translated: A completely new spa experience offers Dutchtub, a hot tub that can be independently set up outside in the garden on the rooftop terrace or by the lake. Due to its light weight is a transportation readily available, eg on the roof rack of a car. The concept is ingenious: In general, the double-tub filled with a standard hose connector with water. Then a fire-steel basket attached to the bottom of the spiral. One can be as accessories are available Glutschale, where required, as a protection on the floor underneath. The cavity in the center of the spiral is filled with wood and this ignited. The heat of the fire can be increased using a wok on top of the spiral launched.
During the heating phase or as a cover after the bath, a lid made of polyester is placed on the tub. For the supply of drinks during the bath is an on-board to shut off the glass with integrated bottle cooler is available (not for the smaller version for two people). Dutchtub is available in six different colors, sturdy and holds like a good boat from a similar material for decades.