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As temperatures drop, many people mistakenly keep curtains closed all day, thinking it retains heat. Instead, opening curtains during sunny days allows sunlight to warm the room, which is then released after sunset. Closing curtains at night creates a barrier against cold windows, reducing heat loss. Simple changes like using thicker rugs and ensuring radiators are unobstructed can enhance warmth. Clean windows let in more natural light, and thermal curtains help minimize heat loss. Thus, opening curtains during the day and closing them at night can significantly improve indoor warmth during cold days.