In the 20th century, museum indoor climates have been conditioned ever more strictly, sometimes beyond guidelines, allowing no fluctuations at all. Among other effects, this has led to excessive energy demands. At the start of the 21st century, interest has increased to condition the indoor climate more reasonable. This study assessed the energy impact of three levels of museum climate control: Reference (21 degrees C/50% RH, no permissible fluctuations), ASHRAE's Class AA, ASHRAE's Class A. Full-scale measurements were conducted in the museum Hermitage Amsterdam for one year. The results show that Class AA saved 49% and Class A saved 63% compared to the Reference setpoint strategy. Moreover, relaxing the climate specifications decreased hourly fluctuations, but increased daily fluctuations. It is highly likely that the overall degradation risk has not significantly changed for most artefacts. (C) 2016 Elsevier B.V. All rights reserved.