Boosting attic insulation gives you the most value for your dollar. Shoot for a rating well above the recommended minimum of R-22. Seven inches of fiberglass or rock wool insulation and 6 inches of cellulose insulation are equal to an R-value of 22. In all but the mildest climates, the agency recommends adding more. While you're at it, insulate your hot water heater. Precut "blankets" are available at home improvement stores and are easy to install on electric heaters.
Adding insulation can cost up to $1,800, and could reduce your heating and cooling bills by more than $100 a year. Water-tank insulation wraps cost between $10 and $20, reduce heat loss by 25 to 45 percent and will save you about $23 a year. To save even more, turn down the thermostat on your water heater, to between 115 and 120 degrees. This can reduce your water-heating expense by another 3 percent.