Whilst some architects engage in energy analysis discussions early in design, in most cases building services engineers carry out modelling and simulation tasks often at late stages of design. Recently, however, a number of large architecture firms have begun promoting and reporting in house use of energy modelling early in design. Effects of broadening energy analysis on architects’ design practice as well as on architects’ conceptions of energy are poorly understood and largely unexamined. The analysis draws on semi structured interviews and focus groups with 35 participants across four large UK architecture firms. Findings indicate energy modelling whilst viewed as beneficial is often approached with caution viewing the client, organisation and the project as determining its initial, ongoing or sporadic use. The study contributes to emerging discussions on energy analysis in architecture as well as the growing agenda on professional judgement and roles of design professions in the built environment. There are also implications for UK built environment energy policy as well as the international energy agenda in particular regarding the performance gap.