Sustainability research about using Information and Communications Technologies (ICTs) to reduce household energy consumption has recently focused on two potential strategies: “smart homes” that rely on sensors and technological innovations to automatically reduce the energy load, and tools that seek to persuade users to change their domestic habits, such as by using eco-feedback devices to raise awareness of the amount of energy used. We propose that there is another approach: support and encouragement of existing best practice within a community to spread it more widely. One such practice is household retrofitting: the installation of domestic environmental technologies (DETs) such as increased insulation, energy efficient boilers, or renewable energy that serve to permanently reduce energy use in a household. We have developed a smartphone application to be used in conjunction with retrofitting open-home events that assists organizers in tracking their event’s impact, whilst also helping users in the decision-making processes that surround retrofitting. This paper provides an overview of the app development process and initial results from in-the-wild testing, whilst also identifying potential areas for future research.