From Houselogic.com:  If you’re cold inside your home this winter, odds are it’s because the heat — which you work hard to pay for — is escaping. It’s rushing out through air leaks that can be difficult to find, both on the interior and exterior of your home. 

Fixing air leaks will make your home more energy efficient. You’ll feel warmer in winter, cooler in summer, and, perhaps best of all, you’ll save on monthly utility bills.  Look here to help figure out where you're losing air.