NFRC-certified steel, with whole-unit U-factors as low as 0.21
PINKYS thermally broken Studio Steel assemblies carry NFRC-certified whole-unit ratings, independently tested and verified. Every assembly ships with its label attached.
The National Fenestration Rating Council is an independent, nonprofit organization founded in 1989 that administers the energy performance certification system for windows, doors, skylights, and commercial facades across the United States. It is accepted by building codes in all 50 states, required for ENERGY STAR qualification, and referenced by ASHRAE 90.1, the IECC, and California's Title 24.
Before NFRC, manufacturers self-reported or omitted energy data, which made product comparison impossible. NFRC established a standardized testing methodology and independent certification process, the same protocols applied to every manufacturer, every product, every time, so the U-factor on a Studio Steel label and the U-factor on any other label mean exactly the same thing, measured the same way, with a trusted name behind them.
NFRC's standard requires the label to ship with the product to serve as the compliance documentation accepted by building departments, energy raters, and code officials. A manufacturer claiming NFRC certification without a label is asking you to take the number on faith; the label is what makes it verifiable. Every rated Studio Steel assembly ships with its NFRC label attached.
NFRC accredits independent simulation laboratories and physical test facilities, then certifies products whose results are submitted and validated through its Certification and Licensing Program. The label is issued only after that validation review, which is what makes it a compliance document rather than a manufacturer's assertion.
Five metrics appear on every NFRC label. For steel, the implications differ from wood, vinyl, or aluminum.
Studio Steel thermally broken assemblies meet the 0.30 prescriptive maximum, down to 0.21
U-factor measures the rate of heat transfer through the complete assembly, frame and glass together, in BTU/hr·ft²·°F. It is the primary thermal insulation metric, and the NFRC value is a whole-unit figure that includes the frame alongside the center of glass. W50 TB assemblies are certified at whole-unit U-factors that meet the most demanding US energy codes, reaching 0.21 on the triple-pane fixed window.
This distinction is critical for steel. Steel is highly thermally conductive, so without interruption a steel frame transfers heat at a rate that can sharply elevate the whole-unit U-factor above the center-of-glass value. A thermally broken steel frame interrupts the conductive path with a non-conducting isolator, which is what closes the gap: often 0.45–0.60 for a non-thermally-broken profile versus 0.28–0.35 for a thermally broken one on comparable glazing.
Code context: Title 24 (2025, current) max 0.27 residential prescriptive in most California climate zones, rising to 0.30 in Climate Zones 6–10 and 15. IECC 2021 max 0.27–0.30 by climate zone. ASHRAE 90.1-2022 typically 0.36–0.45 for most US commercial projects.
Certified from 0.13 to 0.32, specified to the climate and orientation
SHGC measures the fraction of solar radiation that passes through the assembly and enters as heat. It is the primary summer cooling metric and a secondary winter heating metric.
Unlike U-factor, where lower is almost universally better, SHGC is directionally dependent. In hot, cooling-dominated zones (US South, Southwest, California Central Valley) a lower SHGC reduces air-conditioning load, with code requirements typically at or below 0.25. In cold, heating-dominated zones (Northeast, Mountain states, Pacific Northwest) a higher SHGC is beneficial, since passive solar gain reduces heating load. Mixed climates call for orientation-specific specification: lower SHGC on south and west, higher acceptable on north and east.
SHGC is governed primarily by glass selection, the Low-E coating tier, tint, and IGU configuration, rather than by frame material. PINKYS specifies the correct Low-E tier for each project's climate zone and orientation.
Studio Steel SHGC values range from 0.13 on a spectrally selective triple pane to 0.32 on a clear-glazed fixed unit, so the right value can be specified per elevation.
VT measures the proportion of visible light that passes through an assembly. Higher VT means more natural light. The key relationship: Low-E coatings reduce both SHGC and VT, though to different degrees. Spectrally selective coatings such as SB70 are engineered to reduce SHGC more than VT, preserving daylight while controlling solar heat gain.
A Studio Steel W50 TB fixed window with SB70 dual pane achieves SHGC 0.22 while maintaining VT 0.51, a meaningful daylight preservation against a lower-tier coating.
CR measures a product's ability to resist condensation on interior surfaces under standardized temperature and humidity. Higher CR means interior surfaces stay above the dew point at lower interior temperatures and higher humidity.
This is where the thermal break pays a comfort dividend beyond energy efficiency. An unbroken steel frame conducts cold to the interior, creating a cold interior surface that attracts condensation at modest humidity levels. A thermally broken frame holds a warmer interior surface temperature, substantially improving CR.
Studio Steel thermally broken assemblies achieve condensation resistance comparable to high-performance wood windows.
CR benchmarks by product type: non-thermally-broken steel 20–35; thermally broken steel (standard) 35–50; high-performance wood / fiberglass 50–65.
Air leakage measures the rate at which air passes through the assembly under a standardized pressure differential, tested to ASTM E283.
All rated PINKYS Studio Steel assemblies are tested to 0.3 cfm/ft² air leakage, meeting the threshold required by the IECC, ASHRAE 90.1, and California Title 24.
The Testing Protocols Explained
| Standard | Determines | Method |
|---|---|---|
| NFRC 100 | U-factor | THERM finite-element modeling validated against physical testing; accounts for frame geometry, glazing, spacer type, and edge-of-glass effects. The label U-factor is a whole-unit value. |
| NFRC 200 | SHGC and VT | WINDOW software with optical data from the International Glazing Database; accounts for coating properties, angular effects, and frame geometry. |
| NFRC 400 | Air leakage | Physical test to ASTM E283 at a standardized 1.57 psf (75 Pa) pressure differential. |
| NFRC 500 | Condensation resistance | THERM and WINDOW modeling under standardized interior and exterior temperature and humidity conditions.. |
IECC residential prescriptive path
The 2021 IECC requires NFRC-certified U-factors and SHGC values for all fenestration. The International Code Council published the newer 2024 IECC in August 2024, but state adoption lags well behind publication: most states remain on 2021, 2018, or earlier editions, each with different thresholds. Confirm the version adopted in your jurisdiction with a local energy code consultant before specifying to these numbers.
| Climate zone | Representative locations | Max U-factor | Max SHGC | Notes |
|---|---|---|---|---|
| Zone 1 | Miami, Honolulu | 0.40 | 0.25 | Hot / very humid |
| Zone 2 | Phoenix, Houston | 0.40 | 0.25 | Hot-dry or mixed-humid |
| Zone 3 | Atlanta, Los Angeles | 0.30 | 0.25 | Mixed-humid or hot-dry |
| Zone 4 | Baltimore, Seattle | 0.30 | None | Mixed |
| Zone 5 | Chicago, Denver | 0.27 | None | Cool |
| Zone 6 | Minneapolis, Helena | 0.27 | None | Cold |
| Zone 7 | Duluth, Fairbanks area | 0.22 | None | Very cold |
| Zone 8 | Arctic Alaska | 0.22 | None | Subarctic / Arctic |
ASHRAE 90.1 commercial and institutional
ASHRAE 90.1 is the commercial and institutional energy standard referenced by the International Building Code for nonresidential projects. NFRC-certified U-factor, SHGC, and VT values are the required inputs for both the prescriptive compliance path and energy modeling under 90.1. The prescriptive path applies to assemblies covering 0–40% of wall area; projects with higher glazing ratios use the trade-off or energy cost budget path, where orientation and window-to-wall ratio carry additional weight. The table below reflects the nonresidential prescriptive maximums from ANSI/ASHRAE/IES Addendum am to Standard 90.1-2022, approved April 2025. Confirm the code edition adopted in your jurisdiction before specifying to these numbers.
| Climate zone | Fixed max U | Fixed max SHGC | Operable max U | Operable max SHGC | Door max U | Door max SHGC |
|---|---|---|---|---|---|---|
| Zone 0 | 0.48 | 0.21 | 0.62 | 0.19 | 0.83 | 0.19 |
| Zone 1 | 0.48 | 0.23 | 0.62 | 0.21 | 0.83 | 0.21 |
| Zone 2 | 0.45 | 0.25 | 0.60 | 0.23 | 0.77 | 0.23 |
| Zone 3 | 0.38 | 0.25 | 0.54 | 0.23 | 0.68 | 0.23 |
| Zone 4 | 0.35 | 0.34 | 0.43 | 0.31 | 0.63 | 0.31 |
| Zone 5 (a) | 0.32 | 0.38 | 0.39 | 0.33 | 0.63 | 0.33 |
| Zone 6 (a) | 0.31 | 0.38 | 0.38 | 0.34 | 0.63 | 0.33 |
| Zone 7 (a) | 0.28 | 0.40 | 0.35 | 0.36 | 0.63 | 0.36 |
| Zone 8 | 0.25 | 0.40 | 0.31 | 0.36 | 0.63 | 0.36 |
(a) At sites 4,000 ft (1,200 m) or more above sea level, the assembly maximum U-factor may be increased by 0.02 Btu/hr·ft²·°F under the prescriptive path only. Source: ANSI/ASHRAE/IES Addendum am to Standard 90.1-2022, Tables 5.5-0 through 5.5-8, nonresidential vertical fenestration 0–40% of wall.
WINDOWS — BY CLIMATE ZONE
NFRC is the official certification body for ENERGY STAR windows, doors, and skylights. Products meeting ENERGY STAR thresholds qualify through the NFRC program and may be eligible for state or utility rebates. Thresholds below are from the Final Draft Version 7.0 specification; confirm the effective date and any final revisions at energystar.gov before specifying
| Climate zone | Max U-factor | SHGC |
|---|---|---|
| Northern | ≤ 0.22 | ≥ 0.17 |
| North-Central | ≤ 0.25 | ≤ 0.40 |
| South-Central | ≤ 0.28 | ≤ 0.23 |
| Southern | ≤ 0.32 | ≤ 0.23 |
Air leakage: ≤ 0.30 cfm/ft² for windows and sliding glass doors. Source: ENERGY STAR Final Draft Version 7.0, Table 1.
SWINGING & SLIDING DOORS — BY GLAZING LEVEL
| Glazing level | Max U-factor | Max SHGC |
|---|---|---|
| Opaque | ≤ 0.17 | No rating |
| ≤ 1/2-lite | ≤ 0.23 | ≤ 0.23 |
| > 1/2-lite — Northern & North-Central | ≤ 0.25 | ≤ 0.40 |
| > 1/2-lite — Southern & South-Central | ≤ 0.28 | ≤ 0.23 |
Air leakage: ≤ 0.50 cfm/ft² for swinging doors; ≤ 0.30 cfm/ft² for sliding doors. Door thresholds apply by glazing level across all climate zones. Source: ENERGY STAR Final Draft Version 7.0, Table 2.
W50 TB Thermally Broken Steel Swing Door
| Glazing configuration | U-factor | SHGC | VT | Air leakage |
|---|---|---|---|---|
| SB70 dual pane w/ lami | 0.35 | 0.20 | 0.46 | 0.30 |
| Triple pane SB70 / Clear | 0.26 | 0.13 | 0.26 | 0.30 |
W50 TB Thermally Broken Casement Window
| Glazing configuration | U-factor | SHGC | VT | Air leakage |
|---|---|---|---|---|
| SB70 dual pane w/ lami | 0.38 | 0.19 | 0.42 | 0.30 |
| Triple pane SB70 / Clear | 0.31 | 0.13 | 0.24 | 0.30 |
W50 TB Thermally Broken Fixed Window
| Glazing configuration | U-factor | SHGC | VT | Air leakage |
|---|---|---|---|---|
| SB70 dual pane w/ lami | 0.30 | 0.22 | 0.51 | 0.30 |
| Triple pane SB70 / Clear | 0.21 | 0.15 | 0.29 | 0.30 |
Steel Fixed Window - TDL
| Glazing configuration | U-factor | SHGC | VT | Air leakage |
|---|---|---|---|---|
| Dual pane Low-E (standard) | 0.62 | 0.48 | 0.57 | 0.30 |
| Dual pane SB70 | 0.61 | 0.21 | 0.46 | 0.30 |
Steel Fixed Window - SDL
| Glazing configuration | U-factor | SHGC | VT | Air leakage |
|---|---|---|---|---|
| Dual pane Low-E (standard) | 0.45 | 0.53 | 0.64 | 0.30 |
| Dual pane SB70 (9.5mm gap) | 0.43 | 0.23 | 0.52 | 0.30 |
| Dual pane SB70 (12mm gap) | 0.41 | 0.23 | 0.52 | 0.30 |
Steel Swing Door — TDL
| Glazing configuration | U-factor | SHGC | VT | Air leakage |
|---|---|---|---|---|
| Dual pane Low-E (standard) | 0.74 | 0.41 | 0.47 | 0.30 |
| Dual pane SB70 | 0.74 | 0.18 | 0.38 | 0.30 |
Steel Swing Door — SDL
| Glazing configuration | U-factor | SHGC | VT | Air leakage |
|---|---|---|---|---|
| Dual pane Low-E (standard) | 0.56 | 0.46 | 0.55 | 0.30 |
| Dual pane SB70 | 0.55 | 0.20 | 0.44 | 0.30 |
| Tall doors — SB70 (12mm spacer) | 0.53 | 0.20 | 0.44 | 0.30 |
What to reference, verify, and request for building department submittal, LEED, and ENERGY STAR. Reference the certified values as minimums
Reference whole-unit U-factor, SHGC, and air leakage exactly as they appear on the NFRC Certified Label for the specific product configuration, tested per NFRC 400 / ASTM E283. These values, not nominal or center-of-glass figures, are what a building department will check against.
Confirm current thresholds and required standards with your project's code consultant before finalizing spec language, since air leakage and other requirements vary by product configuration and are subject to change.
The NFRC label constitutes the fenestration compliance documentation accepted by US building departments for prescriptive-path projects.
For performance-path projects, PINKYS provides complete product data (U-factor, SHGC, VT, frame area, and glazing area) formatted for CBECC-Res, EnergyPro, eQUEST, and other approved energy modeling platforms.
NFRC-certified U-factor, SHGC, and VT values are standard inputs for energy modeling under LEED v4.1 BD+C.
Consult your LEED AP for credit-specific documentation requirements. PINKYS provides VT and other optical data for LEED documentation on request.
Confirm whether the specified glazing configuration meets ENERGY STAR thresholds for the project's US climate zone (Northern, North-Central, South-Central, or Southern). PINKYS can confirm ENERGY STAR eligibility for any standard glazing configuration at the specification stage.
Thresholds and effective dates are set by ENERGY STAR; confirm current requirements at energystar.gov before specifying.
Frequent Questions
Chat with a PINKYS specialist now!
Sat: 11 AM - 2 PM
Send us a message!