17 Home Sealing Caulk is cheap. On windy days, feel around windows, doors, and exterior walls near the floor, electrical outlets or plumbing penetrations. Seal up your windows and doors with caulking and weather stripping to ensure that you're not wasting energy on heat that escapes through leaks to the outdoors. Caulk works best on small gaps. Your hardware store should have products to close the larger gaps. Use low expansion foam product to seal larger openings. Source: EPA - A DO-IT-YOURSELF GUIDE TO ENERGY STAR HOME SEALING