Drawing on insights from Danish and Australian households, this article explores the role of practical knowledge in shaping the energy-intensive practices of domestic heating and cooling. Alongside technological interventions designed to shift and shed energy consumption, prevailing discourses regarding heating and cooling regularly emphasise the importance of householders rationally and efficiently using energy at home. Conversely, this study shows that householders routinely draw on practical forms of knowledge, including embodied understandings and everyday know-how, as they heat and cool their homes. Drawing on social practice theories, this article presents insights from 28 ethnographic interviews and home tours conducted in Greater Copenhagen, Denmark, and Canberra, Australia. Both sites incorporate emerging smart technologies which aim to shift and shed household energy demand, including through better facilitating resident's management of the indoor climate. While the selected field sites differ importantly in terms of the technologies and infrastructures present, as well as the prevailing cultures and climate, the cross-national analysis shows a conceptual overlap in the way that residents in these divergent contexts draw on their lay understandings to pursue thermally desirable home environments. The findings thereby highlight how in the course of everyday life technical and ostensibly rational forms of knowledge are often contextualised and operationalised through their combination with practical knowledge. As such, this article seeks to complement existing research into the smart infrastructures increasingly involved in household energy management by demonstrating and advocating for a fuller consideration of the role played by practical knowledge and everyday experience.