In the early Middle Ages the inhabitants of Polish territories heated their homes with open furnaces or, rarely, with domed stoves. The 13th c. saw novelties imported from Western Europe - fireplaces and hypocausts. The earliest fireplaces are known from the thirteenth-century palace of Henry the Bearded in Legnica and from the seat of the bishops of Wroclaw at Ostrów Tumski. The hypocaust came to Poland with the Cistercian monks. It originated from the ancient Roman system used to heat baths. In the Middle Ages the underfloor heating system was based on two-chamber furnaces; in the lower chamber wood was burnt, while the upper one, filled with stones, absorbed the heat. The oldest Polish examples of hypocaust were found in the Cistercian monastery in Sulejów, while extended systems of furnaces and pipes are known from Teutonic Order castles. Tile stoves came into use later, in the 14th c. In the oldest stoves tiles were shaped like vessels; they were fixed with the bottom facing the interior of the stove. Such stoves did not have internal channels; the heat from the furnace went up into the chimney draft, heating the sides of the stove. Since the mid 15th c. flat tiles began to be used in stove construction; their faces formed the outside of the stove. Tiles were ornamented, so the stove became an element of interior decoration. Between the 14th and the 18th c. the shape, decoration and construction of stoves changed significantly. The shape and decoration were subject to the current fashion and style in architecture. Changes in the construction of stoves were aimed at maximizing heat efficiency. In the 17th c. the changes consisted mainly in thickening the sides of the stove, which increased the heat-accumulating mass but also the consumption of fuel. In the 18th c. it was believed that thinner stove sides guaranteed better heat efficiency. Eighteenth-century building manuals recommended constructing stoves with internal compartments which were supposed to slow down the flow of combustion products and to prolong the heating of the sides of the stove; they also stressed that it was necessary to save fuel. Fireplaces, which were widespread, did not change so much; only the decoration was adjusted to the current style. Fewest changes can be observed in the construction of hypocausts; it seems however, that since the 16th c. this method of heating was rarely applied, probably because it required a lot of fuel to be effective.