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Read three different measures
U-factor describes thermal transmittance: a lower value means less heat transfer for the same temperature difference. SHGC describes admitted solar heat; visible transmittance (VT) describes admitted visible light. They answer different questions. Confirm the units and rating method before comparing proposals, and do not treat a low SHGC as proof of good insulation.
Source: U.S. Department of Energy / FEMP — Window performance definitions (residential purchasing scope)02
Compare the complete assembly
NFRC whole-product ratings account for the glass, edges and frame. A center-of-glass figure cannot be substituted for an assembly rating. As a practical procurement check, request the exact product configuration, glazing build-up, rating scope and supporting report; identify whether proposed substitutions change that evidence.
Source: National Fenestration Rating Council — Understanding Window U-Factor03
Set a project-specific brief
Our suggested review sequence is to record climate, orientation, occupancy, glazing area, comfort goals and applicable local requirements, then ask the design team to assess energy, glare and condensation together. The cited DOE purchasing guidance concerns residential products; its numerical thresholds must not be applied as commercial facade requirements. ALUCORE supplies no certified performance values in this demo.
Source: U.S. Department of Energy / FEMP — Window performance definitions (residential purchasing scope)