OBJECTIVES: The Victorian Healthy Homes Program investigated the impact of thermal home upgrades on energy and health outcomes in vulnerable, older individuals over winter in Victoria, Australia. DESIGN: A staggered parallel-group randomised control trial design of 984 (764 per protocol (PP)) vulnerable households and 1313 (1015 PP) individuals. The intervention group received their upgrade prior to their winter of recruitment, and the control group received their upgrade after the winter of their recruitment. SETTING: Western Melbourne (metropolitan) and the Goulburn Valley (regional) in Victoria, Australia. PARTICIPANTS: 1000 households were recruited: 800 from western Melbourne (metropolitan) and 200 from the Goulburn Valley (regional). INTERVENTION: A thermal comfort and home energy efficiency upgrade of up to UD3500 per household. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was the change in indoor temperature over winter and the secondary outcomes were changes in quality of life, healthcare use and costs, self-reported health measures, energy use and costs and humidity. RESULTS: A relatively low-cost and simple home upgrade (average cost 2809) resulted in reduced gas consumption (-25.5 MJ/day) and increased indoor winter temperatures (average daily increase of 0.33°C), and a reduction of exposure to cold conditions (<
18°C) by an average of 0.71 hours (43 min) per day. The intervention group experienced improved mental health as measured by the short-form 36 mental component summary and social care related quality of life measured by the Adult Social Care Outcomes Toolkit, less breathlessness and lower overall healthcare costs (an average of 887 per person) over the winter period. CONCLUSIONS: The home upgrades significantly increased average winter indoor temperature, improved mental health and social care-related quality of life and made householders more comfortable while yielding reductions in overall healthcare use and costs. TRIAL REGISTRATION NUMBER: Australian and New Zealand Clinical Trials Registry: ACTRN12618000160235.