Under no circumstances should windows be permanently tilted for ventilation, as this would result in too much heat being lost and no real air exchange taking place. This would automatically increase your heating costs.
It takes up to an hour for the warm air to replace the cold air, as the rooms are significantly cooler than after a quick ventilation. Tilting the window cools the walls, increasing the risk of mold growth.
Windows should be kept closed to keep the heat in, and you should keep windows closed at night during the heating season. Shutters and blinds should also be kept securely closed. This way, less heat escapes at night. Always ventilate thoroughly in the morning!
