THEWOSAN is Vienna´s programme and funding scheme for thermal and energy renovation of existing residential buildings. Through both thermal insulation of buildings and additional measures for their heating systems, a significant reduction of the energy consumption in residential buildings can be achieved. This has the benefits of a reduction of CO₂ as well as air pollutant emissions with linked improvement of the global and local environment. In 2000 a grant was implemented as one measure of Vienna´s Climate Protection Plan KLiP and then updated within Vienna´s Energy Efficiency Program called SEP in 2006. More than 88,300 flats have been renovated by 2011. The reduction of the heating energy demand is on average about 960 GWh per year. The linked CO₂ emission reductions over the whole period are nearly 150,000 tonnes. With THEWOSAN, Vienna has developed a well-accepted, very efficient and successful funding scheme for the renovation of existing residential buildings. Additionally, it was possible to avoid a displacement of the original, often socially less advantaged tenants of old buildings in need of renovation.