Insulation and sealing air leaks are cost-effective ways to improve a home's energy efficiency. The document recommends checking insulation levels in walls, attics, basements and crawl spaces and sealing air leaks around windows, doors, electrical fixtures and other openings. Proper insulation varies by climate zone but can reduce energy costs significantly. Hiring a contractor can help assess a home's insulation needs and calculate the return on investment from energy efficiency improvements.