The research question of this report is “Is it possible to save energy by lowering the bedroom temperatures in winter”. In this paper first the literature on optimum sleeping temperatures is investigated. Then bedroom temperatures and CO2 levels in a cold week in March 2018 are investigated in 16 bedrooms of students of the Master course Technoledge Climate Desing in 2017-2018 of the faculty of Architecture and the Built Environment of the Delft University of Technology. This study shows that it must be possible to save energy by lowering the bedroom temperature in winter. The measured indoor temperatures were much higher than the 16-18°C recommended by several authors, and with appropriate bed covering and bed clothing could be much lower than 18°C and a period of lower temperatures could be more healthy. The thermal sensation of the occupants also suggest that lower temperatures are possible as more occupant perceive the indoor temperature as slightly warm or warm then slightly cool or cold, even when the outside temperatures are below 10 °C. The amount of energy that can be saved depends on the ‘home’ climate of the occupants, with occupants with a warmer ‘home’ climate preferring higher temperatures. The amount of energy that can be saved also depends on the energy label of the building. A better energy label means that there is less energy necessary to heat the room. A better scheduling or control system might supply healthier and lower temperatures as night due to a longer time that the heating is turned of. Opening windows to lower the indoor temperature, which might have health benefits, was not preferred by the students because the room would cool down to much, due to safety concerns or due to noise from outside.@en