The Three Ratings

32-Product Data Table

Sorted by U-factor (lowest first). All products in the Substrata database have ENERGY STAR certification. Frame abbreviations: W/A = Wood/Aluminum, W/V = Wood/Vinyl, FG = Fiberglass, V = Vinyl, Comp = Composite.

U-Factor: What the Numbers Mean

The best U-factors in the database — 0.17–0.24 — come from triple-pane units with wood/aluminum frames. These are also the most expensive products: $900–$3,500/unit. The Andersen E-Series Triple at U-0.17 is the best performer in the dataset.

Double-pane Low-E units cluster at U-0.26–0.30. Most residential projects land here. ENERGY STAR Northern climate zone requires U-0.27 or lower; South-Central and Southern zones allow up to U-0.40. Every window in this dataset qualifies for at least one ENERGY STAR climate zone — most qualify for Northern.

SHGC: Climate-Dependent Selection

SHGC is where most buyers get the selection backward. The instinct is "lower is better" because it means less heat gain. But in cold climates, solar gain through south-facing windows is a free heat source in winter. In those climates, a higher SHGC (0.30+) on south-facing windows is energy-efficient.

The general guidance:

• Hot climates (Zone 1–3): SHGC ≤ 0.25. Minimize solar gain year-round. The Milgard Trinsic at SHGC 0.22 and Renewal by Andersen at 0.20 are the best options in this dataset for hot climates.
• Cold climates (Zone 5–8), south-facing: SHGC 0.35–0.45 on south glass. No products in this dataset reach that range — the best performers top out at 0.48 (Ply Gem Pro Series). For high-SHGC applications, look at products outside this ENERGY STAR–optimized set.
• Mixed climates (Zone 4): SHGC 0.25–0.35 is a reasonable middle ground. Most double-pane Low-E products in this dataset land here.

VT: The Tradeoff with SHGC

Every Low-e coating that reduces SHGC also reduces VT — the coating reflects solar heat but also blocks some visible light. In this dataset, the lowest-SHGC windows (triple-pane units at 0.19–0.23) also have the lowest VT (0.33–0.38). The vinyl windows at 0.28–0.30 SHGC have VT of 0.42–0.48 — significantly more visible light.

For daylit spaces (living rooms, offices, south-facing rooms where occupants want natural light), prioritize VT ≥ 0.40 if possible. The Simonton Impressions at VT 0.45 and Alside Mezzo at 0.44 are strong value options for this use case.

Frame Material Effect on U-Factor

Query Window Data via API

The Substrata API returns u_value, shgc, vt, frame_material, glazing_type, and energy_star for all 43 window products. Filter by max_u_value to find ENERGY STAR qualified products for your climate zone.

GET /v1/products?category=windows&energy_star=true&max_u_value=0.27
Authorization: Bearer sk_sub_your_key

// Returns all ENERGY STAR windows with U-factor ≤ 0.27
// Fields: name, manufacturer, u_value, shgc, vt, frame_material,
//         glazing_type, price_min_usd, price_max_usd

See the full API documentation for the complete parameter list, including min_shgc, max_shgc, and min_vt filters.

Related Resources

• Construction Material Prices 2026 — window prices in context with 11 other categories
• Insulation R-Value Comparison — thermal performance data for 29 insulation products
• All window products — browse the full 43-product catalog
• Window price index — price tracking over time
• Andersen Windows products
• Marvin Windows products
• Pella Windows products