Fresh-r is like breathing window. It fits in a window pane. And keeps the air inside healthy. Without wasting energy. By continuously measuring CO2 and relative humidity the indoor air quality is monitored. If necessary the air is ventilated out. At the same time fresh air is blown in. The heat from the outgoing stale air is transferred to the incoming fresh air with a patented heat exchanger, that uses fine copper wire, with a thermal efficiency of 87%. The performance of the device, i.e. how healthy the air is inside and how much energy is saved, is available to users through smartphone, tablet and PC.