Energy prices are skyrocketing. It is time to make our homes more sustainable and thus save energy. In the summer, our homes use less energy than in the winter. In the summer you are outside more often and the heating does not have to be switched on. In winter, we often keep the windows closed to keep the heat in, but unfortunately problems arise. There is no fresh air coming into our well insulated houses. The lack of fresh air leads to high CO2 levels, which in turn leads to various health complaints.