This paper argues that comfort is a social practice, rather than a stable condition caused by controllable indoor climate parameters. It is based on ethnographic field research in different types of Danish dwelling, which brought to light six comfort practices formulated to inspire the design and engineering of indoor climates and environments. The concept of comfort practices is of major importance when the goal is to change private energy consumption patterns towards a sustainable future. This investigation extends the existing body of research about the relation between comfortable indoor climate conditions and human health, productivity and energy costs with a practice-oriented approach to understanding what indoor climate and comfort means to people in their everyday lives. This practice-oriented perspective on product design recognizes that practices unfold over time and space, and hence call for both quantitative and qualitative research methods (e.g. data sets, statistics, market research, ethnographic accounts of situated practice) (Shove, 2006). Recent research in the design discipline, in the areas of