The traditional hot tub is built of wood. Back in the old palaces and castles there were also such baths in use. However, those hot tubs were without the stove and the water was heated separately. Modern hot tubs are equipped with wood burning or electric heaters to heat up the water into certain temperature. Hot tubs are made in various sizes for 2 to 10 people, the most popular are the wooden hot tubs made for up to 6 people.