In order to meet global challenges to reduce greenhouse gas emissions, the implementation of solar systems for residential purposes is an emergent task. Commonly liquid-based solar systems are used to heat up shower and pool water. More recently space heating systems have become part of sustainable buildings. An alternative could be a solar system that uses air as energy carrier. This study analyses the retrofit of such a system into a 40-year-old building. Starting from the analysis of the energy demand of a selected room, a solar air heater was designed, simulated and evaluated experimentally. The solar efficiency of the constructed collector reached 60%.