Key takeaways
- NFRC ratings cover energy performance (U-factor, SHGC, VT, condensation resistance), while NAFS ratings cover structural, water and air performance; a US or Canadian permit usually needs both.
- A NAFS rating such as CW-PG50 means the CW performance class with a design pressure of 50 psf (about 2,394 Pa), structurally proof-tested at 150% of design pressure.
- Minimum performance grades are PG15 for R, PG25 for LC, PG30 for CW and PG40 for AW, and only AW also requires life-cycle testing.
- Multiply an NFRC U-factor in Btu/h·ft²·°F by 5.678 to get W/m²K, so U-0.20 equals about 1.14 W/m²K.
- Canada additionally requires CSA A440S1, the Canadian supplement, which sets air (A2, A3, Fixed), water (B-ratings) and wind ratings from local climatic data.
In the United States and Canada, a window needs two separate kinds of evidence. NFRC ratings give its energy performance: U-factor, SHGC, visible transmittance and condensation resistance, certified and printed on an NFRC label. NAFS (AAMA/WDMA/CSA 101/I.S.2/A440) gives its structural, water and air performance as a class and grade such as CW-PG50. Canada adds the CSA A440S1 supplement, and ENERGY STAR sets voluntary U-factor and SHGC limits by climate zone.
Two systems, two questions
NFRC (the National Fenestration Rating Council) answers how much heat and light the window lets through. NAFS answers whether it stays in the opening, keeps water out and limits air leakage under a given wind pressure. US energy codes (IECC and state codes) reference NFRC ratings, and residential and building codes reference NAFS for structural and water performance. A window can have excellent NFRC numbers and a weak NAFS grade, or the other way round. Never accept one as a substitute for the other.
NFRC ratings and what each number means
| Rating | NFRC procedure | Unit and typical range | What it tells you |
|---|---|---|---|
| U-factor | NFRC 100 | Btu/h·ft²·°F, roughly 0.15–1.20 | Whole-product heat loss; lower is better |
| SHGC | NFRC 200 | 0–1, typically 0.15–0.60 | Fraction of solar heat admitted; lower reduces cooling load |
| Visible transmittance (VT) | NFRC 200 | 0–1, typically 0.30–0.70 | Daylight admitted; higher is brighter |
| Air leakage (AL) | NFRC 400 | cfm/ft², often ≤ 0.3 required | Infiltration at a reference pressure |
| Condensation resistance (CR) | NFRC 500 | 1–100 | Resistance to interior condensation; higher is better |
NFRC certification is a programme, not a single test. An accredited simulation laboratory models each product line in THERM/WINDOW at the standard size for that product type. An accredited test laboratory validates the simulation with a hot-box test. A licensed inspection agency (IA) inspects the plant and authorises labels. Certified products are listed in the NFRC Certified Products Directory (CPD). Each unit carries a temporary label with U-factor, SHGC and VT, and the IA's permanent marking ties the window to its certification record.
ARCVIEW's NFRC record, NFRC-ARC-24-0731 (Intertek certified simulation, July 2024), covers the C80 tilt-turn and S120 lift-and-slide. The best rated configuration is U-0.20, SHGC 0.27, VT 0.48 and CR 68. A U-factor of 0.20 converts to about 1.14 W/m²K. This is higher than the 0.9 W/m²K EN Uw for the same C80, because NFRC uses different standard sizes, boundary conditions and calculation rules. Our U-value and SHGC guide explains the difference.
NAFS: performance class, grade and design pressure
| Class | Typical application | Minimum performance grade | Structural test at minimum grade (150% of DP) |
|---|---|---|---|
| R | One- and two-family dwellings | PG15 (15 psf ≈ 718 Pa) | 22.5 psf ≈ 1,077 Pa |
| LC | Low- and mid-rise multi-family, light commercial | PG25 (25 psf ≈ 1,197 Pa) | 37.5 psf ≈ 1,796 Pa |
| CW | Low- and mid-rise commercial, heavier use | PG30 (30 psf ≈ 1,436 Pa) | 45 psf ≈ 2,155 Pa |
| AW | High-rise, institutional, heavy use; life-cycle tested | PG40 (40 psf ≈ 1,915 Pa) | 60 psf ≈ 2,873 Pa |
The performance grade (PG) is the design pressure (DP) in psf that the product passed. Its tests are a uniform-load deflection test at DP, a uniform-load structural test at 150% of DP with limits on permanent set, a water penetration test at a fixed percentage of DP (typically 15%, with a minimum of 2.86 psf / 137 Pa), and an air-leakage test. Air leakage is limited to about 0.3 cfm/ft² (1.5 L/s·m²) at 1.57 psf for R, LC and CW, and is stricter for AW. Forced-entry resistance and operating force are also checked. A product can carry an optional DP higher than its PG, for example ‘CW-PG50, DP +60/−70’, when the structural and water results differ.
Ratings apply only to the tested size and configuration, which is why one system family can carry several. ARCVIEW's NAFS report WH-104672913-001 (Intertek · Warnock Hersey, March 2024) records AW-PG70, a 70 psf design pressure, 10.5 psf water and forced-entry Grade 40 for the C80, S90 and P100 families. The standard C80 casement datasheet quotes CW-PG50. Always match the report's tested size and configuration to the window on your drawings.
ENERGY STAR climate zones
| Zone | Covers, broadly | Max. U-factor | SHGC |
|---|---|---|---|
| Northern | Northern states, mountain West | ≤ 0.22 (with trade-off options down to 0.20) | ≥ 0.17 at 0.22; any at ≤ 0.20 |
| North-Central | Mid-Atlantic and central states | ≤ 0.25 | ≤ 0.40 |
| South-Central | Upper South, parts of the Southwest | ≤ 0.28 | ≤ 0.23 |
| Southern | Gulf Coast, Florida, southern Arizona | ≤ 0.32 | ≤ 0.23 |
Canada: CSA A440S1 and the National Building Code
In Canada, NAFS is used together with CSA A440S1, the Canadian supplement. It sets the required performance from the building's site: the driving-rain wind pressure and the 1-in-50 hourly wind pressure from the National Building Code climatic data, building height and exposure. It reports ratings in Canadian terms, with air leakage as A2, A3 or Fixed and water as a B-rating. Energy performance is rated under CSA A440.2 and NFRC procedures, often stated in metric. ARCVIEW's CSA A440S1-19 report ITS-CA-24-11908 (Intertek Canada) records A3 air, B7 water and C5 wind for the C80 and CW150 systems. See our Canada market page.
What importers need for a permit
- NFRC temporary label on every unit, with the product listed in the NFRC Certified Products Directory.
- NAFS test report or certification showing class, grade and design pressure at or above the size installed.
- Permanent NAFS or certification label where the building code or authority having jurisdiction requires it.
- CSA A440S1 ratings for Canadian projects, checked against the project's climatic data.
- Impact test reports (ASTM E1886/E1996) and state approvals such as Florida Product Approval in wind-borne-debris regions.
- Shop drawings, anchorage calculations and installation instructions; many authorities want these stamped by a locally licensed engineer.
Codes and adopted editions vary by state, province and municipality, and they change. Confirm the required ratings with the authority having jurisdiction before ordering. For US projects, see our USA market page, or send us your schedule and we will map each unit to its report.
Frequently asked questions
- What is the difference between NFRC and NAFS?
- NFRC rates energy performance: U-factor, solar heat gain coefficient, visible transmittance, air leakage and condensation resistance, shown on the NFRC label. NAFS (AAMA/WDMA/CSA 101/I.S.2/A440) rates structural, water penetration and air leakage performance as a class and grade, such as CW-PG50. US and Canadian building permits generally need both, because energy codes and structural codes reference different standards.
- What does CW-PG50 mean?
- CW is the NAFS performance class for commercial windows. PG50 is performance grade 50, meaning the window passed a 50 psf (about 2,394 Pa) design pressure, a structural test at 75 psf (150% of design pressure), and water and air tests at the levels the standard ties to that grade and class. The rating applies to the tested size and configuration.
- How do I convert an NFRC U-factor to W/m²K?
- Multiply the U-factor in Btu/h·ft²·°F by 5.678. U-0.20 is about 1.14 W/m²K, and U-0.30 is about 1.70 W/m²K. The conversion only changes units. NFRC and EN ISO 10077 use different standard sizes and boundary conditions, so the same window usually rates somewhat worse under NFRC than its European Uw.
- Is ENERGY STAR mandatory for windows in the US?
- No. ENERGY STAR is a voluntary programme. Building codes such as the IECC set mandatory maximum U-factor and SHGC values, which are often less strict than ENERGY STAR in cold zones. ENERGY STAR matters for incentives, utility rebates and some green-building programmes. Products must have NFRC-certified ratings to qualify, and criteria are updated periodically.
- Does Canada accept US NAFS test reports?
- NAFS is a joint US-Canadian standard, so the same test can serve both markets. Canada also requires the CSA A440S1 supplement, which sets the required performance from site climatic data in the National Building Code and reports air (A2, A3, Fixed), water (B-ratings) and wind ratings in Canadian format. Check provincial and municipal requirements with the local authority.
Sources & standards
- 01National Fenestration Rating Council: ratings, labels and Certified Products Directory — NFRC
- 02AAMA/WDMA/CSA 101/I.S.2/A440 North American Fenestration Standard and AAMA certification — Fenestration and Glazing Industry Alliance (FGIA)
- 03CSA A440S1 Canadian Supplement and CSA A440.2 energy performance standards — CSA Group
- 04ENERGY STAR residential windows, doors and skylights — U.S. Environmental Protection Agency / ENERGY STAR
- 05International Energy Conservation Code and International Residential Code — International Code Council
