Yes, you describe exactly the kind of house I live in. The problem with the upper floor is that there's a skylight which you can't shade. The sun can shine on t

Yes, you describe exactly the kind of house I live in. The problem with the upper floor is that there's a skylight which you can't shade. The sun can shine on the floor (with the floor heating underneath) and warm it up all day. You don't even need to open a window to let the heat in. The air ventilation system uses a heat exchanger to keep the heat in during winter. I am still not sure as to what it does during summer. It surely doesn't feel like it makes it actively hotter, but it also doesn't cool it down. We are required to have this system running all the time (on the lowest level). Otherwise the house would begin to mold quickly as there is absolutely no natural air flow when the windows are closed. In fact, I once deactivated the system because of bad air quality outside. It was unbearable within about two hours inside. It's really a bit weird, but on the other hand, I like that I don't have to think about opening the windows to ventilate the house and it helps keep the heating costs low during winter.