Neither -- it's often in excess of 100 degrees in the summer, so it's pretty silly to leave the windows open to that kind of air. We have good insulation in the house for a reason, and it's not just for the extreme cold in the winter. We'll generally keep the windows and doors open in the early morning and again after the sun goes down if the temp falls below the inside temperature, and keep everything closed during the day with the curtains drawn and run a fan for a bit of air flow. There's a newer portion of our house that has quite a few windows; it gets very hot in the summer no matter what we do, so we don't use it much. However, our office and the kids' rooms were all wetwall, built circa World War I, so it stays nice and cave-like in there if we keep everything closed.