Introduction This essay examines the building and management of Nationalmuseum in Stockholm. Today the building has just recently been reopened after years of renovation and fitting of a new system that will control the indoor climate. This means deep interventions in a nineteenth-century building that was not designed to be airtight or to be heated all year around. The renovation gives a reason to ponder on how the building originally was designed and constructed, but also how it was managed over time. The climate of the house has been an issue ever since the building was constructed in the early years of the 1860s. It was fitted with a central heating system already then, but the building proved difficult to heat in winter and to ventilate in summer. There were continuous problems with dehydration of organic materials in the art collections in winter-time, and with too much sunlight exposing fragile art in the warmer season. Curiously, the introduction of artificial humidification first around 1930 and then again in the 1950s did not solve the problem of dehydration. On the contrary climate problems became ever more complex around the mid-20thcentury because of the introduction of motor traffic with its exhausts, and increasing demands on a stable indoor climate in art museums. How did museums balance the needs of their collections, against the needs of staff and visitors? What considerations where made when choosing heating and ventilation for a museum at this time? In order to illuminate these questions, archival sources from Nationalmuseum, Riksarkivet (National State Archives) and the engineering and architectural company SWECO have been used. Överintendentsämbetet (Board of Public Works and Buildings, abbreviated ÖIÄ) was the custodian of government buildings, followed by Kungliga Byggnadsstyrelsen (Board of Building and Planning, abbreviated KBS) after an organizational shift in 1918. The museum was thus responsible for the management of its collections but not of its building. Until 1939 there was also a second museum housed in the bottom floor: Statens Historiska Museum, the National Historical Museum. If the museum had a complaint on the performance of the building or the heating system, it would have to notify ÖIÄ (or KBS after 1918), which then would decide how to act. Judging by archive sources, it becomes evident that ÖIÄ had small means to make more demanding interventions in existing buildings, and often complaints seem to have been more or less ignored because of lack of resources. By studying the correspondence it is possible to gain a better understanding of how museum management perceived indoor climate and how ÖIÄ responded. The purpose of the essay is to explore how the construction and management of the indoor climate was shaped by technological development and how views on the running of a museum building shifted. Nationalmuseum was fitted with a hot water central heating system. In the early 1860s this was something hardly heard of in Sweden at this time. In general, the central heating systems used at that time were caloriphers, furnaces that heated the air that was then circulated through the building. There were firms in Stockholm installing piping, but none of them was considered competent enough to do the installations in Nationalmuseum. Most entrepreneurs in Stockholm worked with gas piping, not with water or sewer piping.[1]In the early 1860s it was still not evident that a public building should be equipped with this kind of heating, despite the relatively long and cold winters in Stockholm. Public buildings in general were heated with local fireplaces, most often tile stoves produced in the city. Today it is well known that control of indoor climate is key to the management of collections. Too much heat makes the air dry, which may cause damage to fragile objects such as paintings on panels or wooden furniture with veneer. Too little heat makes the air very humid, which promotes mold, vermin, corrosion and rot. What is considered "too little" or "too much", however, has changed since the nineteenth century.[2]The essay explores why central heating was installed in the museum, what the expectations on its functioning were, and how building and museum management (they were – and are – separate from each other) continuously commented on its performance in the decades following the opening of the museum, up until the 1970s when air pollution had become a serious problem demanding a technical solution. [1]G. Stålbom, Varmt och vädrat. VVS-teknik i äldre byggnader, Sveriges VVS Museum – SBUF – VVS Företagen, Stockholm 2010, 15. In 1861 Stockholm opened its first waterworks with 30 km of piping. [2]M. Legnér, "Conservation versus thermal comfort – conflicting interests?: The issue of church heating, Sweden c. 1918–1975",Konsthistorisk Tidskrift 2014 (e-publication ahead of print). Kulturarvet och komforten: frågan om lämpligt inomhusklimat i kulturhistoriska byggnader under 1900-talet