This essay deals with heating installations put into medieval Gotland churches from the 1920s to the early 1950s. Focus is on the work of the restorer Erik Johan Fant (1889–1954) who was the most frequently engaged restorer of churches in Sweden from c. 1925 to 1950. His work has not been the subject of much academic research. The essay covers how Fant and authorities involved in the restorations perceived the aesthetical and practical issues of installing modern heating systems in medieval churches. It also places Fant’s work in the wider context of heating for comfort and conservation purposes in churches. Our knowledge of heating systems used in churches in the past is very limited: on what grounds was a certain system chosen, how was it designed, and what consequences did it have for the conservation of the church? From having been solely an issue of increased comfort and pleasing design, the development of heating technology increasingly involved the interests of conservation. In the first half of the 20th century, central or electric heating was introduced in many stone churches, but often without any analysis of the risks involved. Still in the 1920s, the typical Gotland church was heated with just one or two ovens. They were still not electrified. Two problems especially were connected to overheating before the 1950s: first the soiling of walls and vaults, and second the desiccation of organic materials, particularly painted wooden objects. Central heating, especially in the form of low pressure steam which was common before 1945, certainly made these damages worse. Despite these issues, almost all of the 2,700 churches in Sweden had some kind of heating installed by the mid-1950s, and the reason was that heating primarily was perceived by the Swedish Church as a matter of comfort. Shortly after the end of the period in question, damages caused by heating would attract more attention from the developing conservation field. / <p>Alternate Title: The church -- "a machine for sitting": the introduction of heating systems into medieval Gotland churches during the early 20th century. (English)</p> / Kulturarvet och komforten: frågan om lämpligt inomhusklimat i kulturhistoriska byggnader under 1900-talet