Weatherizing a home is the process of improving its airtightness and its ability to retain heated and cooled air, and it does not have to be massively expensive or terribly difficult. A well-sealed, well-insulated home is more comfortable and energy-efficient, and it’s also cheaper to run.Below, we walk you through the basic steps that experts we spoke with—independent researchers, home energy contractors, and a utility representative—suggest as the most cost-effective ways to weatherize. Some of the tips are even things you can do yourself without special tools or skills. Taken together, they can potentially lower your utility bills by as much as 40%, ultimately paying for themselves.