I think you're under-estimating how hot it gets inside well-insulated European homes. Your mileage may vary across European countries, but in the north where it gets cold in the winter our homes are built to trap heat. Opening windows won't get you very far as the temperature radiates through the windows and traps in the walls. Closing blinds will help, but not by much. It got over 40c in my office this summer. This is not livable conditions with a fan.