Never understood how people sleep in warm rooms. 15 C is ideal for me, hell, I usually leave my window open at night to keep the room nice and cool. I guess it

Never understood how people sleep in warm rooms. 15 C is ideal for me, hell, I usually leave my window open at night to keep the room nice and cool. I guess it doesn't get too cold where I am (high of 9 C, low of -1 usually in winter), but my place doesn't have any insulation at all, or double glazed windows, and I use the heater for only 30 minutes a day usually in winter, because I just put on more clothes.