In the UK, finances and resources are invested into the application of new technologies, construction materials and control systems for homes, with the aim of improving energy efficiency. One such example is the experimental BASF house, built to study the thermal performance to achieve a comfortable home that uses energy efficiently. The house includes low to zero carbon (LZC) technologies that are promoted to reach a higher level within the UK Code for Sustainable Homes (CSH). For this study a mixed-methods sequential explanatory design (Creswell JW. Research Design. Qualitative, Quantitative, and Mixed Methods Approaches, 3rd edn. Sage Publication, 2009; Nataliya VI, Creswell JW, Stick SL. Using mixed-methods sequential explanatory design: from theory to practice. Field Methods 2006; 18: 3) that has been developed in the field of social and behavioural sciences has been applied, consisting of two distinctive phases: quantitative and qualitative. The rationale behind is for the quantitative data and its analysis is used to understand system performances while the qualitative data explain the numerical results in-depth, through the subjects in study, the occupants' perceptions. This article presents conclusions from an investigation into the use and performance of a biomass boiler and passive design features, derived from a live-in experience in a well-insulated and airtight CSH Level 4 home over two consecutive winter periods (2008-9 and 2009-10), which is part of on-going research project. The study also discusses a number of issues regarding the effective efficiency and appropriateness of the systems, which were selected based on a desire to comply with regulations for a better rated home rather than on their user friendliness and comfort for the occupants of a sustainable home; jeopardizing people's safety in times.