Editor’s introduction: With energy prices rising again, many homeowners are planning energy-efficiency improvements to their homes. But most people are unsure of where to begin, and even seasoned builders don’t always know which priorities should rise to the top of the list. Betsy Pettit, an architect at Building Science Corporation , recommends starting where you can get the most bang for the buck.Step 4: Replace your windowsTable of Contents:1. The Basement2. The Roof3. The Walls4. The Windows5. Mechanicals6. Appliances7. Renewable EnergyWith the bottom and top of the house sealed and insulated, as well as the walls, windows represent the next opportunity. Old windows often leak both air and water into the house. They might not open and close properly, and are sometimes be obscured by unattractive storm windows and screens that reduce the amount of light that can enter. Moreover, they rarely have low-e glazing.Properly installed Energy Star (or better) windows seal the holes in the walls to keep out water and weather extremes. If high-quality glazing is specified, the windows can admit useful solar gain during the winter, while still preventing excessive heat loss at night. To prevent summer overheating, the best glazing for east and west windows is usually low-solar-gain glazing.Properly specified new replacement windows should reduce your energy bills. Since replacement windows are expensive, though, don’t expect a fast payback on your investment. But if you decide to replace your windows, at least you can enjoy higher comfort from Day One.This article is adapted from Betsy Pettit’s Remodeling for Energy Efficiency in Fine Homebuilding magazine. FURTHER RESOURCES:In Green Basics: WindowsIn Product Guide: Window Shades In Strategies and Details: Upgrade Existing Windows In Blogs: Making the Case for Triple-Glazed Windows Choosing Triple-Glazed Windows Passivhaus Windows High-Solar-Gain Glazing Should I Replace My Windows? Tax Credits for Window Replacement Windows That Perform Better Than WallsIn Fine Homebuilding: Get the Right Replacement Windows Should Your Old Wood Windows Be Saved?