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Proper ventilation is important, as this can save you money during the colder months of the year. Instead of tilting a window for longer, it should be opened wide for a couple of minutes. This allows you to ban the humid air from the room, without having furniture and walls lose their heat. After having ventilated the room, you will notice that it heats up way easier. This has a simple reason: dry air has a lower heat capacity and therefore heats up faster!