The paper argues that existing computer programs for thermal predictions do not produce suitable information for architects, particularly at the early stages of design. It reviews the important building features that determine the thermal environment and the need for heating and cooling plant. Graphical design aids are proposed, with examples to show the summer conditions in naturally ventilated buildings. It is shown that it is not realistic to consider thermal conditions in isolation: the feasibility of achieving the desired natural ventilation rate and the use of artificial lighting are also important. Sample design aids are included for these aspects. (Author)