Window performance ratings are the numbers printed on the sticker of every new window, and they tell you more about comfort, energy bills and durability than any showroom pitch.
Most homeowners peel that sticker off on day one. Read it before you sign instead: window performance ratings are the only place two quotes can be compared on the same terms.
This guide decodes all seven window performance ratings: five on the energy label, plus the structural and sound ratings on a second sticker or the spec sheet. Tap through the sample label and walk into your next estimate knowing what to ask.
Match U-factor and SHGC to your ENERGY STAR climate zone first. Then compare daylight, air leakage and condensation resistance between quotes, and ask for the performance grade and sound rating in writing.
What’s In This Guide
Where Window Performance Ratings Actually Live
No single sticker holds everything. Window performance ratings are split across three places, and a complete quote should point you to all three.
The NFRC Sticker
The NFRC label carries the energy numbers, measured the same way for every brand.
- U-factor0.20–1.20
- Heat gain (SHGC)0–1
- Visible transmittance0–1
- Air leakage≤ 0.3
- Condensation resistanceoptional
The Performance Grade
A second label, tested to AAMA/WDMA/CSA 101/I.S.2/A440, shows how the unit handles wind, water and air.
- Performance classR · LC · CW · AW
- Performance gradePG + number
The Sound Rating
Sound rarely makes the sticker. Look for a Sound Transmission Class (STC) on the spec sheet.
- Sound Transmission ClassSTC + number
- Higher meansquieter
Tap a Field to Decode It
This sample label pulls all seven window performance ratings onto one sheet. Tap a field to see what it measures, the Ohio target and the question to ask.
U-Factor
Field 01 · lower is betterHow well the whole window keeps heat from escaping a room. NFRC ratings typically fall between 0.20 and 1.20.
ENERGY STAR asks for 0.22 or lower in the Northern zone, with trade-offs up to 0.26, and 0.25 or lower in North-Central.
“Is this the U-factor for the exact size and glass package I’m buying?”
Heat Gain Coefficient (SHGC)
Field 02 · depends on zoneHow much of the sun’s heat gets through, from 0 to 1. Lower blocks more.
In the Northern zone ENERGY STAR sets a floor of 0.17, so some winter sun still counts. North-Central caps it at 0.40.
“Can we tune the glass for west-facing rooms that overheat in summer?”
Visible Transmittance
Field 03 · higher is brighterHow much daylight comes through, from 0 to 1. Coatings, tints and wide frames pull it down.
ENERGY STAR sets no minimum. Compare it between quotes so a lower SHGC doesn’t quietly cost you a darker room.
“How much daylight do I give up with this coating compared with the standard glass?”
Air Leakage
Field 04 · lower is tighterHow much outside air gets through the window itself, in cubic feet per minute per square foot of window.
ENERGY STAR windows must rate 0.3 or lower in every zone. Lower than that is a plus for drafty, windy sites.
“How will the gap between the new frame and the opening be sealed and insulated?”
Condensation Resistance
Field 05 · optional ratingHow well the window resists water forming on the interior surface. NFRC lists it as optional, so not every label shows it.
There’s no ENERGY STAR minimum. Higher is better, and it matters most in kitchens, baths and bedrooms in January.
“Does this unit use a warm-edge spacer, and can you show me its rating?”
Performance Grade
Field 06 · higher is strongerA set of air, water and structural requirements tied to a design pressure range, measured in pounds per square foot.
It depends on height, exposure and local code. An open lot sees more wind than a sheltered street.
“What class and PG is this unit certified to, and does it meet code for my address?”
Sound Transmission Class
Field 07 · higher is quieterA single number for how well the unit blocks airborne sound, calculated from lab testing across many frequencies.
Compare it when a bedroom faces a busy road, a school or a flight path.
“Is this STC from a lab test of the full window, or just the glass?”
Window Performance Ratings for Ohio Homes
ENERGY STAR splits the country into four climate zones, and the window performance ratings it requires change with each one. Ohio homes fall in the Northern zone or, along the Ohio River, the North-Central zone. Your county decides, so check the Climate Zone Finder on the ENERGY STAR windows page before you compare quotes.
Here are the targets from the ENERGY STAR Version 7.0 specification:
| Path | U-factor | SHGC | What it means |
|---|---|---|---|
| Northern, standard | ≤ 0.22 | ≥ 0.17 | The main target for most of the Miami Valley |
| Northern, trade-off | 0.23–0.24 | ≥ 0.35 | Slightly higher U-factor, offset by more winter sun |
| Northern, trade-off | 0.25–0.26 | ≥ 0.40 | Same idea, with a higher SHGC floor |
| North-Central | ≤ 0.25 | ≤ 0.40 | River counties, where summer heat gain counts more |
| All zones | Air leakage ≤ 0.3 | Cubic feet per minute per square foot | |
The surprise in the Northern zone: ENERGY STAR sets a minimum SHGC, not a maximum. A window that blocks nearly all of the sun’s heat can miss the mark here, because winter sunshine through south-facing glass is warmth the furnace doesn’t have to make. Read both window performance ratings together, never U-factor alone.
The Glass Behind the Numbers
Window performance ratings don’t come from the frame color or the brand name. They come from parts working together: the glass coating, the gas between panes, the edge spacer and the frame.
The U.S. Department of Energy’s Energy Saver guide says low-emissivity coatings can cut energy loss by as much as 30% to 50%, and spectrally selective coatings filter out 40% to 70% of the heat that normally comes through while keeping full daylight. That’s why two window performance ratings, SHGC and visible transmittance, can move apart.
The same guide notes that warm-edge spacers lower U-factor and reduce condensation at the edge of the glass. Our guide to gas-filled windows covers the argon or krypton layer, and the look at benefits of vinyl windows explains how the frame shapes the whole-unit number.
Wind and Sound: The Other Two Ratings
Energy numbers get the attention, but two more window performance ratings decide how a unit handles a storm and how quiet a bedroom feels.
Built for the Wind It Will See
The Fenestration and Glazing Industry Alliance defines a performance grade as a set of requirements tied to a design pressure range. Every unit also carries one of four performance classes:
- R
- LC
- CW
- AW
FGIA says the class is chosen on performance, not building type. The water test scales with the rating: 15% of design pressure for R, LC and CW, and 20% for AW. Strong gusts are part of life here, as our Dayton wind damage guide shows.
Quiet You Can Compare
STC is a single number calculated under ASTM E413 from lab sound-transmission tests run under ASTM E90. A higher STC means the window blocks more airborne sound.
Ask whether the number belongs to the full window or only to the glass. Some spec sheets also list OITC, a related outdoor-indoor rating. Sound is the quietest of the window performance ratings, and the easiest to forget.
Red Flags on a Window Quote
- No label numbers at all. “High-efficiency glass” is a phrase, not one of the window performance ratings. Get U-factor, SHGC and visible transmittance in writing.
- ENERGY STAR with no zone. Version 7.0 criteria change by climate zone, so “ENERGY STAR certified” only means something next to the zone it was certified for.
- A design pressure with no PG. FGIA notes some products were marketed on design pressure alone. A performance grade means the unit passed the full set of tests, not just one.
- Glass-only numbers. NFRC window performance ratings cover the whole product, frame included. A glass spec alone flatters almost any window.
- No plan for the install. Window performance ratings describe the unit, not the gaps around it. Ask how the opening will be flashed, sealed and insulated.
The Takeaway Worth Sharing
Read the sticker before you sign, not after the install. Seven window performance ratings tell you more than any sales pitch.
Send this to the friend comparing two window quotes this month.
Got a Quote? Let’s Read the Label Together
Thrush & Son®: family-owned exterior pros since 1960.
If you’re in the Miami Valley and want window performance ratings explained on a real home, read the Thrush & Son® guide to ENERGY STAR replacement windows, then book an in-home consultation.
➡️ Schedule in Dayton➡️ View All ServicesCall (937) 833-5136 · 115 Jefferson St, Brookville, OH 45309
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Further Reading
Official sources: NFRC, ENERGY STAR, the ENERGY STAR Version 7.0 specification, the U.S. Department of Energy, FGIA and ASTM International.
Window Performance Ratings FAQ
What are window performance ratings?
They are standardized numbers that describe how a window handles heat, sunlight, daylight, air, condensation, wind and sound. The energy ratings appear on the NFRC label, and the structural and sound ratings come from a separate label or the spec sheet.
Which window rating matters most in Ohio?
Start with U-factor and SHGC together, matched to your ENERGY STAR climate zone. In the Northern zone that means a U-factor of 0.22 or lower with an SHGC of at least 0.17, or one of the listed trade-offs.
Is a lower SHGC always better?
No. In the Northern zone, ENERGY STAR sets a minimum SHGC because winter sun helps heat the house. A lower number helps most on west-facing glass or in the North-Central zone, where it is capped at 0.40.
What does PG mean on a window?
PG stands for performance grade, a set of air, water and structural requirements tied to a design pressure range. A higher PG means the unit was tested to handle more wind pressure.
Where do I find a window’s STC rating?
Usually on the manufacturer’s spec sheet, not with the other window performance ratings on the sticker. Ask whether it comes from a lab test of the full window under ASTM E90, with the rating calculated under ASTM E413.
Written by Corey Thrush, Vice President and third generation of Thrush & Son®.
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