Abstract: A jacket of rigid thermal insulation, containing a thermally reflective coating on its inner surface, is movably mounted on a hot water tank (gas-, electric-, oil-, etc- fired, of either standard or special design) mounted in a sauna room and selectively covers the top and sides of the tank and extends to the supporting surface of the tank. The jacket is selectively movable to a closed position completely enclosing the tank and to an open position exposing part of the top, sides and bottom of the tank and part of the area between the supporting surface and the bottom of the tank. A perforated housing is provided in the area between the supporting surface and the bottom of the tank. Sauna rocks and electric heating elements are provided in the perforated housing. An electric fan is mounted in the area for directing hot air from the housing upward around the tank.