Is It Worth Replacing Windows for Energy Savings?

Replacing windows for energy savings pays off best when the old windows are single-pane. ENERGY STAR says certified windows lower household energy bills "by an average of up to 13 percent nationwide when replacing single-pane windows." If your windows are already double-pane, or replacement is mainly about cutting drafts, cheaper steps often come first. Caulking and weatherstripping often pay for themselves within a year, according to the US Department of Energy (DOE), and low-E storm windows can save a similar amount of energy for much less money. The best way to decide is to compare options with numbers for your own climate.

Updated: October 2026.

What the official figures say

The table lists the savings figures that EPA and DOE publish for each option, with the basis each agency states. The figures are national or test-home averages, not a forecast for your house.

Two points stand out. First, the large published savings all start from single-pane or low-performing windows. ENERGY STAR describes single-pane windows as "poor performers at insulating against cold weather" that "typically do not have coatings to block solar heat in the summer." Second, a storm window over an existing window can capture much of the same benefit for less money, which is why ENERGY STAR calls certified storm windows "an affordable option for homes where full window replacement may be difficult."

When replacement is more likely to be worth it

• You have single-pane windows. This is the case behind the largest published savings figures.
• The windows need replacing anyway. If you are replacing for another reason, the energy question becomes a smaller one: how much more does an efficient unit cost than a standard one? For federal buyers, DOE's Federal Energy Management Program (FEMP) calculated that ENERGY STAR-qualified residential windows save money over their life if they cost no more than $2 per square foot more than less efficient models. That is federal procurement guidance, not a household quote, but it gives a sense of scale for the price premium.
• Comfort matters to you. ENERGY STAR says that with certified windows "the interior glass stays warmer" in winter and that most certified windows "reduce the 'heat gain' into your home" in summer. It also notes that certified windows "are more resistant to condensation, but even they can suffer from it in cold weather."

When to try cheaper options first

• Drafts around the frame. Air sealing comes first. DOE describes caulking and weatherstripping as simple air-sealing techniques with quick returns.
• Sound single-pane or older windows you want to keep, for example in a historic house. Low-E storm windows can go on the outside or the inside of the existing window. ENERGY STAR certifies storm windows on emissivity, solar transmittance and air leakage, with criteria that vary by climate zone.
• Double-pane windows in good condition. The published replacement figures are based on single-pane windows, so they don't tell you what replacing double-pane windows would save. Check that with a calculation for your climate before you buy.

If you replace, buy for your climate

The two ratings that drive energy use are on the NFRC label: U-factor, where lower is better, and solar heat gain coefficient (SHGC), where the right value depends on your climate. ENERGY STAR recommends:

• Northern US: "lower U-factor windows (0.22 and less)"
• The South: "lower SHGC levels (0.23 and less)"

Under ENERGY STAR Version 7.0, effective October 23, 2023, the U-factor limits are 0.22 (Northern), 0.25 (North-Central), 0.28 (South-Central) and 0.32 (Southern), and each zone has its own SHGC limit. Find your zone with the ENERGY STAR climate zone finder. Then confirm a product's certified ratings in the NFRC Certified Products Directory or the ENERGY STAR Product Finder. For how coatings and spacers affect these numbers, see low-E glass and spacers and window energy efficiency.

Check the numbers for your home

National averages can't tell you what a window will save on a north wall in Minneapolis or a west wall in Houston. The GlassBase window energy calculator estimates heating and cooling energy for a window at your ZIP code, using typical-year weather data and the orientation you choose.

1. Enter your ZIP code and the window's wall direction.
2. Set up a configuration close to your current window, then a replacement option, choosing the frame material, profile system, glazing and spacer.
3. Compare the calculated heating and cooling energy in kWh. Start with kWh, because your utility rate decides the dollar value, and rates vary by state and plan.
4. Change one option at a time, such as glazing or orientation, to see which change matters most where you live.

The calculator's values are engineering estimates, not NFRC ratings. See how the GlassBase window performance simulator works. Before you buy, confirm the actual product's ratings on its NFRC label.

Bottom line

Replacing single-pane windows with certified, climate-appropriate windows is where the official savings figures are largest. If your windows are sound, seal the air leaks first and price low-E storm windows as an alternative. If you replace, choose by U-factor and SHGC for your ENERGY STAR zone, and check the savings for your ZIP code before you commit. To compare installers and manufacturers, browse window companies by city. Terms used here are defined in the glossary.

Estimate the savings for your ZIP code

Sources

• US EPA, ENERGY STAR, Residential Windows, Doors and Skylights (up to 13% when replacing single-pane windows; comfort and condensation statements)
• US EPA, ENERGY STAR, High Performing Windows or Storm Windows (single-pane windows; storm windows about 20% and about 3-year payback; U-factor and SHGC advice by region)
• US EPA, ENERGY STAR, Storm Windows (storm windows about 10% and about 3-year payback; interior and exterior types; certification criteria)
• US EPA, ENERGY STAR, Residential Windows, Doors, and Skylights Version 7.0 (zone limits; effective October 23, 2023)
• US DOE, Performance Validation of Low-e Storm Windows (September 30, 2015)
• US DOE, Insulation and Air-Sealing Essentials (October 29, 2024; caulking and weatherstripping)
• US DOE, FEMP, Purchasing Energy-Efficient Residential Windows, Doors, and Skylights (cost-effectiveness for federal purchasers)
• NFRC, Certified Products Directory