Fuel poverty affects around 34% of European homes, representing a considerable burden to society and healthcare systems. This pilot study assesses the impact of an intervention to install a new first time central heating system in order to reduce fuel poverty on household satisfaction with indoor temperatures/environment, ability to pay bills and mental well-being. In Cornwall, 183 households received the intervention and a further 374 went onto a waiting list control. A post-intervention postal questionnaires and follow-up phone calls were undertaken ( n = 557) to collect data on household demographics, resident satisfaction with indoor environment, finances and mental well-being (using the Short Warwick-Edinburgh Mental Wellbeing scale). We compared responses between the waiting list control and intervention group to assess the effectiveness of the intervention. A total of 31% of participants responded, 83 from the waiting list control and 71 from the intervention group. The intervention group reported improvements in the indoor environment, finances and mental well-being. However, these benefits were not expressed by all participants, which may result from diverse resident behaviours, lifestyles and housing characteristics. Future policies need to consider whole house approaches alongside resident training and other behaviour change techniques that can account for complex interactions between behaviours and the built environment.