Heat from your home is leaked into your walls through electrical outlets and switch plates. To prevent this, install inexpensive foam gaskets (from home improvement stores).
[For more easy, money-saving, Eco-friendly tips, download a FREE copy of Green Riches: Help the Earth & Your Budget. Go to https://www.smashwords.com/books/view/7000, choose a format, and download to your computer or e-book device. For a description of the book go to My Free Books).