NJ Window Ratings Explained
U-factor, SHGC, VT, AL, CR — what every number on the NFRC label means, what to target for NJ's Northern climate zone, and which numbers actually matter for your heating bill.
Every modern window has an NFRC (National Fenestration Rating Council) label listing five performance ratings. Most homeowners ignore them. They shouldn't — these five numbers are the difference between a window that saves you $400/year on heating bills and one that doesn't. NJ falls in ENERGY STAR's Northern climate zone, which has specific minimum requirements for each rating. Here's the decoder.
What each NFRC rating means
U-Factor
0.18 – 0.50 (lower = better)→ Target for NJ: ≤0.22 (ENERGY STAR Northern zone) or ≤0.25 (North-Central)
How much heat escapes through the window. The single most important number for NJ (cold-climate state where heating cost is the biggest energy expense). Standard double-pane with low-E + argon: ~0.27–0.30. Triple-pane: 0.18–0.22. Single-pane: ~1.0 (catastrophically inefficient). New Jersey is split between two ENERGY STAR climate zones. Bergen, Passaic, Morris, Sussex, Warren, Hunterdon and Somerset are Northern, where current ENERGY STAR v7.0 criteria are U-factor ≤0.22 with SHGC ≥0.17; the rest of the state is North-Central at U-factor ≤0.25 with SHGC ≤0.40. ENERGY STAR also certifies Northern-zone windows on an equivalent-performance path — U-factor 0.23 or 0.24 at SHGC ≥0.35, and 0.25 or 0.26 at SHGC ≥0.40 — so don't reject a 0.25 window on U-factor alone until you've read its SHGC.
SHGC (Solar Heat Gain Coefficient)
0.10 – 0.80 (varies by use)→ Target for NJ: ≥0.17 for ENERGY STAR Northern zone; 0.20–0.30 typical for NJ
How much solar heat passes through the window. NJ's Northern zone wants SHGC ≥0.17 (let some winter sun in to reduce heating) but you don't want it too high either (summer cooling load). South and west-facing windows: aim for 0.25–0.35 (controlled solar gain). North and east-facing: lower (0.20–0.25) is fine since solar gain is minimal anyway. Wrong SHGC for the elevation = either uncomfortable summer rooms (too high) or higher heating bills (too low).
VT (Visible Transmittance)
0.20 – 0.80 (higher = brighter)→ Target for NJ: ≥0.40 for most residential
How much visible light passes through the glass. Higher VT = brighter, more natural daylight; lower VT = darker rooms. Most modern double-pane with low-E: 0.50–0.60. Triple-pane: slightly lower (0.45–0.55). Privacy/obscure glass: 0.30–0.50. Tinted glass: 0.20–0.40. For residential, you almost always want VT ≥0.40 to avoid dark interior spaces. The trade-off: lower VT often correlates with lower SHGC (less heat, less light).
AL (Air Leakage)
0.01 – 0.30 (lower = better)→ Target for NJ: ≤0.30 for ENERGY STAR; ≤0.10 typical for premium
How much air leaks through the window assembly per square foot per minute under standard test pressure. Lower = tighter. Standard residential: 0.15–0.25. Premium fiberglass and aluminum-clad wood: 0.05–0.10. Higher AL = drafty windows, higher heating bills, condensation risk. Required to be ≤0.30 for the ENERGY STAR label. AL matters more in NJ winter than most other ratings — a window with great U-factor but high AL still feels drafty.
CR (Condensation Resistance)
1 – 100 (higher = better)→ Target for NJ: ≥50 for NJ Northern zone
How well the window resists interior-side condensation in cold weather. Important in NJ January and February when single-digit overnight temperatures cause interior moisture to condense on cold glass surfaces. Standard double-pane: 50–65. Triple-pane: 70–80. Single-pane: 30–40 (will frost over in NJ winters). CR is optional on the NFRC label but worth asking about for cold-climate spec.
NFRC label questions
Where do I find these numbers on a window quote?
On the NFRC (National Fenestration Rating Council) label — every certified window has one attached to the unit and listed on the manufacturer spec sheet. Quote should reference the specific NFRC numbers for the spec'd unit. If a quote doesn't reference NFRC numbers, ask for them in writing — anything else is the contractor hiding the actual performance spec.
What's the difference between ENERGY STAR and ENERGY STAR Most Efficient?
ENERGY STAR certification is the baseline. Under current v7.0 criteria that's U-factor ≤0.22 with SHGC ≥0.17 and AL ≤0.30 in New Jersey's Northern zone (Bergen, Passaic, Morris, Sussex, Warren, Hunterdon, Somerset), and U-factor ≤0.25 with SHGC ≤0.40 in the North-Central zone covering the rest of the state. Most Efficient is a tier above certification, with tighter limits that EPA reissues — read the current criteria on energystar.gov rather than any contractor's summary of them. One thing worth knowing: Most Efficient used to be the tier the federal 25C tax credit required. That credit was repealed for anything installed after 12/31/2025, and no NJ utility program we checked rebates replacement windows at all, so Most Efficient no longer unlocks any money in New Jersey. It's a performance tier now, nothing more. Cost adder over standard ENERGY STAR: roughly $50–$150 per window depending on manufacturer line.
Should all my windows have the same SHGC?
No — and this is where lazy quotes fail. South and west-facing windows should have controlled solar gain (SHGC 0.25–0.35) to balance winter heat-gain benefit with summer cooling-load cost. North-facing can be lower SHGC (0.20–0.25) since solar gain is minimal anyway. We spec SHGC per-elevation on every quote — not a single number applied to the whole house.
Is U-factor more important than SHGC in NJ?
Yes, generally — NJ winters are colder than summers are hot, and heating cost is the bigger annual expense. U-factor reduction has a larger impact on annual energy bills than SHGC reduction in NJ. That said, both matter; ignoring SHGC entirely creates summer-overheating problems on south/west exposures. Spec both intentionally.
What's the realistic minimum spec I should accept in NJ?
ENERGY STAR certification for your actual zone — U ≤0.22 with SHGC ≥0.17 in the Northern counties, U ≤0.25 with SHGC ≤0.40 in North-Central — with AL ≤0.30, double-pane low-E with argon. Below this is throwing money away on energy bills over the window's lifespan. Above this — Most Efficient or triple-pane — pays back faster in cold-climate north NJ (Sussex, Warren, Morris) than central/south. Don't accept any quote that doesn't list specific NFRC numbers.
Quotes that list NFRC numbers per opening
Every Precision Windows quote lists the U-factor, SHGC, VT, AL, and CR for each window — spec'd per-elevation so south/west get different SHGC than north. Compare against any contractor who quotes without the numbers.