This PhD thesis looks at the issue of heating historic churches. These structures pose particular challenges: they consist of large high volumes, they are composed of materials that are vulnerable to changes in indoor microclimate, they usually possess fabric of low energy efficiency, it is often very difficult to insert new systems without damaging the historic fabric, and they are only very intermittently occupied. Churches are thus particularly difficult to heat satisfactorily; most early churches were entirely unheated. Later, local heating, such as stoves, were introduced to respond to congregations’ demand for comfort. Newer churches then started being built with heating systems from the start. Although these were rarely satisfactory, modern solutions have generally either attempted to provide low-level continuous background heating or concentrated on heating the congregation or a combination of the two. This thesis starts by looking at existing systems for heating churches and the current literature used to establish so-called best practice. It then sets out to investigate whether these solutions are actually working. It starts by establishing the ideal environmental conditions for conservation of the fabric. It uses existing literature on the conservation of museum artefacts, looking at each material found in churches in turn to map the various requirements and see if a set of conditions can be found that will ensure preservation of all the materials involved. Next, the thesis uses monitoring to establish what conditions actually exist in historic churches. Four churches in Cambridge were chosen to conduct an on-site survey. The four case studies adopt different modern heating solutions and each was carefully monitored throughout the year to establish what the exact conditions were. At the same time the thesis recorded thermal comfort and energy performance. There has been no study that brings together information on proper environmental conditions for protection of all the various categories of materials, perceived thermal comfort and energy performance in church buildings so this thesis sets out to provide one. The thesis shows that most modern heating strategies for historic churches fail to satisfy all three strands of environmentally sustainable performance indicators for church buildings, i.e. energy performance, thermal comfort, and the preservation of the historic fabric. It ends by tentatively suggesting how these challenges might be approached. The final section of the thesis details the limitations of the study and the various areas that require further study. Overall the study seeks to provide a useful survey of the existing literature on the subject and raise some important questions about the current strategies being employed for heating historic churches. Although the study is restricted to examples in a relatively small geographical area, the conclusions could be applied generally to other Northern European examples and the implications apply not only to other churches but also similar large-volume historic buildings such as town halls, dining halls and guild halls all over Europe.