Energy-Efficient Windows: Replace, Repair or Add Storm Windows?

Energy-efficient windows can make a home quieter, less drafty and cheaper to heat and cool. But they are one of the most expensive energy upgrades, and the savings alone rarely pay for them quickly. This guide explains how to read window ratings, what ENERGY STAR requires in your climate, honest payback math, and when repair or low-e storm windows are the smarter buy.

Should you replace, repair or add storm windows?

Replace windows that are rotted, broken, fogged between panes, or painted or swollen shut. If the frames and sashes are sound, repair them and add weatherstripping, caulk or low-e storm windows instead. ENERGY STAR says storm windows cost about one-quarter to one-half as much as common replacement windows, with much lower installation costs.

Here is a quick way to compare your options. Savings and costs are from ENERGY STAR and DOE where noted; your results will vary with climate, home and energy prices.

Start with the cheap fixes no matter what. Our guide to sealing air leaks covers caulk and weatherstripping, and a home energy audit can show whether your windows are really the biggest problem. In many homes, the attic and basement leak far more air than the windows.

What do U-factor and SHGC mean on the NFRC label?

The National Fenestration Rating Council (NFRC) label shows tested energy ratings for a specific window. The two that matter most are U-factor, which shows how well the window keeps heat in, and solar heat gain coefficient (SHGC), which shows how much of the sun’s heat gets through. Lower is better for both in most cases.

NFRC lists five ratings that may appear on its label:

The NFRC label rates the window unit as built. It does not cover leaks between the window frame and your wall, which depend on how carefully it is installed.

What do ENERGY STAR windows require in your zone?

ENERGY STAR splits the country into four window zones: Northern, North-Central, South-Central and Southern. Each has maximum U-factor and SHGC limits, and all certified windows must have air leakage of 0.3 cubic feet per minute per square foot or less. Products must also be independently tested and certified by NFRC.

These are the current ENERGY STAR criteria for residential windows (ENERGY STAR criteria tables dated October 2023, accessed October 2026):

In the North, ENERGY STAR allows a slightly higher U-factor if the window lets in more free solar heat in winter. In the South, the low SHGC limit matters most, because keeping out the sun’s heat cuts air conditioning use. ENERGY STAR’s window zones are not the same as the eight climate zones used for insulation, so look up your window zone separately on the ENERGY STAR criteria page.

Frames and glass

ENERGY STAR does not require any specific technology, so certified windows come in vinyl, wood, fiberglass, composite and aluminum frames. Double- or triple-pane glass, low-e coatings, gas fills between panes and insulated spacers all help a window hit its rating. Rather than comparing features, compare the NFRC numbers for the size and style you need.

How much do new windows save, and what is the payback?

ENERGY STAR says certified windows lower household energy bills by an average of up to 13% nationwide when they replace single-pane windows. Savings are much smaller when you replace double-pane windows. With replacement windows starting around $400 each and often costing far more, the energy payback usually takes decades.

ENERGY STAR’s Home Upgrade page estimates replacements start at about $400 per window for a simple, energy-efficient 3 ft by 5 ft double-hung window, and premium options can reach about $1,600 per window or more. Installation complexity, custom sizes, trim repair and lead-safe work in older homes all push costs up.

An honest payback example

Here is a simple, hypothetical calculation to show the math. It is an illustration, not a prediction for your home.

1. Say your household energy bills total $2,000 a year, and you replace all single-pane windows.
2. A 13% saving would be about $260 a year. That is ENERGY STAR’s “up to” average, so yours could be lower.
3. Say you replace 15 windows at $400 to $1,600 each. That is $6,000 to $24,000.
4. Simple payback is the cost divided by yearly savings: about 23 years at the low end and over 90 years at the high end.

That is why ENERGY STAR advises getting quotes from several installers and why replacement makes most sense when windows need replacing anyway. Comfort, noise, safety and appearance are real benefits too; just don’t buy windows expecting them to pay for themselves fast. Ask each installer for a written quote listing each window’s U-factor and SHGC.

Are low-e storm windows a better deal?

For many homes with sound single-pane windows, yes. EPA estimates ENERGY STAR low-e storm windows installed over single-pane glass with no existing storms save about $350 a year in heating and cooling, roughly 10% nationally. ENERGY STAR expects the extra cost over non-certified storms to pay back in about three years.

A storm window is a second window mounted on the inside or outside of your existing one. It adds a layer of glass and a still air space and blocks drafts. ENERGY STAR certified storm windows use low-e glass and must meet emissivity, solar transmittance and air leakage limits for their climate zone under a specification that took effect September 5, 2018.

Key facts from ENERGY STAR and DOE:

• Over single-pane windows: about $350 a year in heating and cooling savings, roughly 10% nationally (EPA estimate, which it calls conservative because it excludes air leakage savings).
• Upgrading old clear-glass storms: swapping them for ENERGY STAR low-e storms saves about another $50 a year, roughly 2%.
• Research results: a 2015 DOE summary of research found that a low-e storm window over a low-performing window can reduce heating and cooling costs by 10% to 35%, at about a quarter of the cost of full replacement.
• Interior or exterior: both types qualify. Exterior storms must have weep holes or similar features so water can drain, and storms with thermal breaks are recommended over metal-framed windows.

Storm windows are a good fit for historic homes, for owners who want to keep original wood windows, and for budgets that cannot stretch to full replacement. Interior storms can also suit renters, with the landlord’s permission.

What low-cost fixes help drafty windows?

Caulking, weatherstripping and plastic window film kits are the cheapest window upgrades. ENERGY STAR rates window film as an easy one-day DIY project under $100. Caulking and sealing around window and door trim is a moderate-to-difficult DIY job. These steps cut drafts right away and make any later storm window or replacement work better.

1. Caulk the trim: ENERGY STAR says to use caulk for gaps of 1/4 inch or less. Clean the crack, apply a steady bead, and smooth it with a finger or tool.
2. Fill bigger gaps: use foam backer rod or a non-expanding foam made for windows and doors, so you don’t bow the frame.
3. Weatherstrip the sashes: add or replace weatherstripping where the sash meets the frame and where the two sashes meet in a double-hung window.
4. Lock the window: on double-hung windows, the latch pulls the sashes together and tightens the seal.
5. Add plastic film for winter: size the film with a few inches to spare, clean the frame, apply the tape, then shrink the film tight with a hair dryer.
6. Use window coverings: cellular shades and heavy curtains closed at night in winter, and shades closed on sunny summer afternoons, reduce heat flow.

In homes built before 1978, painted window parts may contain lead. EPA’s Renovation, Repair and Painting rule requires contractors paid to disturb painted surfaces in those homes to be certified in lead-safe work practices. If you do the work yourself, avoid dry sanding and scraping and follow EPA’s lead-safe guidance.

What about energy-efficient exterior doors?

A good exterior door matters less for energy than the windows or attic, but a tight seal helps comfort. ENERGY STAR certifies doors based on how much glass they have. Solid doors without glass must have a U-factor of 0.17 or lower, and doors with more glass have limits that vary by climate zone.

ENERGY STAR door criteria (tables dated October 2023):

• Opaque (no glass): U-factor 0.17 or lower, all zones.
• Half-lite or less glass: U-factor 0.23 or lower and SHGC 0.23 or lower, all zones.
• More than half-lite glass: U-factor 0.26 or lower and SHGC 0.40 or lower in Northern and North-Central zones; U-factor 0.28 or lower and SHGC 0.23 or lower in South-Central and Southern zones.
• Air leakage: 0.3 or less for sliding doors and 0.5 or less for swinging doors, in cubic feet per minute per square foot.

Before replacing a door, try new weatherstripping, an adjustable threshold and a door sweep. Those fixes cost little and often stop most of the draft.

Can you get a tax credit or rebate for windows in 2026?

There is no federal tax credit for windows, skylights or doors installed in 2026. The 25C Energy Efficient Home Improvement Credit does not apply to property placed in service after December 31, 2025, under Public Law 119-21. Some utilities offer window or storm window rebates, so check locally.

If your windows or doors were placed in service in 2025, you may still claim 25C on your 2025 return using Form 5695: 30% of the cost, up to $600 for windows and skylights and $250 per exterior door ($500 total for doors), within the $1,200 annual general limit. ENERGY STAR notes exterior windows and skylights had to meet its Most Efficient criteria, and the IRS required a qualified manufacturer identification number for property placed in service in 2025. Confirm details with the IRS or a tax professional, and see our 2026 guide to energy tax credits.

State Home Energy Rebates programs focus on whole-home savings, insulation, air sealing and electric appliances, and windows are not on the HEEHR appliance rebate list. HOMES programs reward modeled or measured whole-home savings, so check your state’s rules in our state-by-state rebate guide before assuming windows count.

Bottom line

Energy-efficient windows are worth buying when your old ones are failing, and ENERGY STAR models rated for your zone are the right choice when you do. But on energy savings alone, they pay back slowly. For sound windows, caulk, weatherstripping and low-e storm windows usually deliver more savings per dollar. For a ranked list of upgrades that pay off faster, see our guide to lowering your energy bill.