One of the biggest energy hogs in the home during the fall and winter months is heat, whether it's from oil or electricity. While sealing up cracks in windows and doors is one way to prevent warm air from escaping, here's one culprit you may not have thought about: your kitchen and bathroom ventilation fans. Yes, they are useful for removing steamy heat or cooking odors from inside the home, but if they are left on for too long, they also suck out warm air. This causes your heating system to work harder to keep your home warm. Use the ventilation systems for a few minutes and shut them off to save money and energy.