The direct and indirect health effects of increasingly warmer temperatures are likely to further burden the already overcrowded hospital emergency departments (EDs). Using current trends and estimates in conjunction with future population growth and climate change scenarios, we show that the increased number of hot days in the future can have a considerable impact on EDs, adding to their workload and costs. The excess number of visits in 2030 is projected to range between 98-336 and 42-127 for younger and older groups, respectively. The excess costs in 2012-13 prices are estimated to range between AU$51,000-184,000 (0-64) and AU$27,000-84,000 (65+). By 2060, these estimates will increase to 229-2300 and 145-1188 at a cost of between AU$120,000-1,200,000 and AU$96,000-786,000 for the respective age groups. Improvements in climate change mitigation and adaptation measures are likely to generate synergistic health co-benefits and reduce the impact on frontline health services.