ENERGY STAR Window Ratings: What You Should Know

ENERGY STAR-certified windows can save you hundreds on energy bills while keeping your home comfortable year-round. Unlike vague “energy-efficient” claims, ENERGY STAR labels provide specific measurements, such as heat transfer and air leakage, that directly impact your comfort and wallet. Homeowners who install properly rated windows typically cut their energy bills by 12% — a noticeable difference when those summer or winter utility bills arrive.

Swapping old single-pane windows for ENERGY STAR models can save you between $101 and $583 yearly, depending on where you live, according to the Department of Energy. Over the 20+ year lifespan of highly efficient windows, those savings add up to thousands, often exceeding what you paid for the windows in the first place.

But you shouldn’t go with just any ENERGY STAR-certified window. ENERGY STAR labels specify clear standards — and your climate should influence what you select. “My customers know they want ENERGY STAR windows, but they’re surprised when I explain that Florida windows would freeze a Michigan home,” said Mark R., who’s installed windows for six years at Big C Lumber across Indiana, Michigan, and Ohio.

Below, we’ll discuss how to read an ENERGY STAR label, how these certified windows can benefit you, and how to choose an energy-efficient window that’s right for your home.

What Do ENERGY Star Ratings Mean for Windows?

Windows earn ENERGY STAR certification by meeting strict performance standards set by the U.S. Environmental Protection Agency (EPA). What works in Arizona fails miserably in Minnesota, so the requirements vary by region — something I wish I’d known before buying my first set of replacement windows.

For a window to earn the ENERGY STAR seal, it needs to:

• Pass rigorous testing in National Fenestration Rating Council (NFRC)-certified labs (not just manufacturer claims)
• Hit specific heat retention and solar gain targets for your climate zone
• Keep air leakage minimal (no more than 0.3 cfm/ft²*)
• Resist condensation that can damage window frames
• Come with clear instructions for proper installation

*Cfm/ft² stands forcubic feet per minute per square foot.

Some manufacturers throw around terms like “high-efficiency,” but ENERGY STAR certification backs up those claims with hard numbers. In my experience installing windows in older homes, the difference between certified and noncertified windows becomes obvious during the first extreme weather season.

How To Read an ENERGY Star Rating

An ENERGY STAR label can tell you how that window will perform in your particular climate. You’ll want to note measurements such as U-factor and air leakage.

U-Factor

The U-factor shows how well your window keeps heat from escaping. The scale runs from 0.20 to 1.20, and unlike most ratings, lower numbers are better. For folks living in cold climates, you want something below 0.30 to avoid watching your heating dollars fly out the window.

Most homeowners find their sweet spot between 0.25 and 0.30 — the point where performance and price align nicely. During bitter January mornings, you’ll appreciate those low U-factor numbers. The physics behind it involves heat transfer rates rather than the R-value you might know from insulation. Multiple glass panes with gas between them and special coatings work together to achieve those lower numbers.

Solar Heat Gain Coefficient (SHGC)

SHGC tells you how much summer sun turns into indoor heat through your windows. On a scale from 0 to 1, lower numbers mean less heat sneaking in, which keeps your AC from working overtime. Homeowners in warmer climates will want a mere 0.25 SHGC, while homeowners in colder regions might prefer 0.40+ to capture free winter warmth.

I’ve seen dramatic differences in cooling bills between homes with appropriate and inappropriate SHGC ratings. Your west-facing windows particularly need the right rating. Some windows use specialized tints or microscopic metal coatings that block heat while still letting in plenty of daylight.

Visible Transmittance (VT)

VT measures daylight passing through your window. Ratings range from 0 to 1, with higher numbers letting in more natural light. Most ENERGY STAR windows fall between 0.30 and 0.70, balancing light and energy concerns.

Higher VT values mean fewer lights switched on during daytime, adding to your energy savings. The best windows use selective coating that blocks heat while welcoming light. In my living room, I chose windows with higher VT and have rarely needed lights before sunset since.

Air Leakage (AL)

Air leakage measures how much air sneaks through the window assembly joints. Look for ratings between 0.1 and 0.3, with lower numbers meaning less draft. ENERGY STAR windows must score 0.3 or less.

Poor scores here translate directly to uncomfortable drafts and wasted energy. Quality windows use effective weatherstripping and tight manufacturing tolerances to minimize this movement. You’ll feel the difference on windy days when your curtains stay still instead of dancing.

ENERGY STAR Ratings by Region

The U.S. has four distinct window climate zones, each with its own certification requirements:

Up in the Northern Zone (such as in Minnesota and Maine), windows should trap precious heat with U-factors of 0.30 or less. These windows should allow more solar heat gain to help with winter warming.

The North-Central Zone covers states like Ohio and Nebraska, where windows need to juggle seasonal changes. They require decent insulation (a U-factor equal to or less than 0.30) with moderate solar control.

Down in the South-Central region (Texas and Tennessee), the emphasis shifts toward keeping cooling costs down. These windows should block more solar heat while providing reasonable insulation for occasional cold snaps.

The Southern Zone (Florida and Hawaii) cares almost exclusively about rejecting solar heat. Windows there need the lowest SHGC values (less than or equal to 0.25), but they can get by with less insulation since freezing rarely happens.

As someone who’s lived in Indiana and spent a lot of time in Texas, I can vouch for how differently windows perform across these regions. The wrong window in the wrong place costs you money every month.

Benefits of ENERGY-Star Rated Windows

ENERGY STAR windows provide real-world advantages such as lower bills and noise reduction. Here’s what makes them worth the slightly higher upfront cost.

Lower Energy Bills

How much your bills will decrease depends on your existing windows and the specific windows you replace them with.

In my previous home, I noticed my utility bills dropped noticeably when I replaced my old windows with ENERGY STAR ones. The new windows had a better thermal barrier, and in my 2,200-square-foot home, my energy bill decreased by about 12% per month.

Improved Home Comfort

Know that spot near the window you avoid during weather extremes? ENERGY STAR windows eliminate those hot and cold zones. They maintain more consistent room temperatures and prevent the condensation that leads to mold and damage.

When I upgraded the windows in my old home, I noticed a difference right away. I no longer had to wipe moisture away from the window seals or felt a draft when I walked past them.

Environmental Benefits and Home Value

By reducing energy waste, these windows shrink your carbon footprint by about 2,000 pounds of CO2 annually per home, roughly what a car produces in two months of driving.

They can boost your property value when you sell your home, too. Many real estate agents will tell you that energy-efficient windows are one of the top home improvement factors that help homes sell faster.

Noise Reduction

The features that boost your windows’ efficiency also block outside noise from coming in. Multiple panes and quality seals reduce outside noise by up to 40% compared to single-pane windows.

For my bedroom, which faced a busy street, this benefit proved almost as valuable as the energy savings. Traffic sounds, neighbor noise, and even barking dogs became much less intrusive. I’ve slept better and felt less stressed since upgrading.

How To Choose an Energy-Efficient Window

Finding the right energy-efficient windows for you requires more than just looking for an ENERGY STAR label. You should ensure that the U-factor and SHGC suit your climate needs. You’ll also want to take into account window material, glass features, and styles.

Costs in this section are sourced from contractor estimates used by Angi.

Match Windows to Your Climate

Where you live should drive your window choices. Northern homeowners should focus on the U-factor, aiming for 0.30 or lower to keep heat inside during winter. If you’re in the South, prioritize a low SHGC (0.25 or less) to block summer heat. If you’re somewhere in the middle, you’ll generally want to balance both ratings around 0.30.

Select the Right Frame Material

To choose a window frame material, consider your budget and home style, as well as your performance and maintenance needs. For example, vinyl is low maintenance but doesn’t allow for much customization, while wood requires more maintenance but can be painted more easily.

• Aluminum ($75–$400): These provide strength at a lower cost but conduct heat and cold unless they include thermal breaks. I suggest avoiding these except for in very mild climates.
• Vinyl ($100–$900): These offer effective heat retention at reasonable prices. They won’t rot or need painting, but they come in fewer color options.
• Wood ($150–$1,300): Nothing beats wood frames for classic charm and natural insulation. They require occasional maintenance but add warmth and character to older homes.
• Fiberglass($500–$1,500): I chose this for my bathroom for its moisture resistance and better thermal properties. These don’t expand or contract much and can be painted any color.

Choose Glass Package Features

Modern window glass technology makes a huge difference in performance:

• Double panes create an insulating pocket between glass sheets.
• Low-emissivity (low-e) coating acts like sunscreen for your home, blocking heat while allowing light.
• Gas fills like argon or krypton provide better insulation than plain air.
• Warm-edge spaces reduce heat loss around the edge of the glass.

Consider Window Style and Operation

The way in which windows open affects their energy performance:

• Casement windows (my personal favorite for windy areas) crank outward and seal tightly when you close them.
• Double-hung windows slide up and down, offering traditional looks but potentially more air leakage.
• Picture windows stay fixed in place, providing the best efficiency for scenic views.
• Sliding windows move horizontally — convenient but typically less airtight.

Most homes look best with a mix of styles. I used casements in areas needing ventilation and picture windows where the view matters most.

Factor in Installation Quality

I’ve seen the best windows perform terribly when installed carelessly. Professional installation adds $100–$300 per window but pays for itself through proper performance and valid warranties.

When getting quotes, don’t forget installation costs. Proper installation must include:

• Precise leveling and squaring
• Proper insulation in gaps
• Correct flashing to keep water out
• Complete sealing of all joints

After watching an installer take three hours to perfectly set a single window, I understood why DIY installation often leads to problems.

Next Steps

Check your existing windows for telltale problems. Drafts, condensation, or fogging between panes signal it’s replacement time. Before shopping, grab measurements and photos of your current windows, then ask dealers specifically for ENERGY STAR options rated for your region.

“The biggest mistake homeowners make is rushing window decisions,” Mark R. said. “Take time to compare U-factors and SHGC ratings between brands, even if they all have the ENERGY STAR label.”

I recommend getting at least three quotes from local installers who specialize in energy-efficient windows — not just general contractors.