By Patriot Home Service. Published: . Updated: . Published by Patriot Home Service.
Learn what U-factor, solar heat gain coefficient and air leakage tell you, and why room exposure still matters.
Learn what U-factor, solar heat gain coefficient and air leakage tell you, and why room exposure still matters.
U-factor describes heat transfer through a window; a lower value generally means less heat transfer under the rating conditions. Solar heat gain coefficient describes how much solar energy passes through; the desired value depends on climate, orientation and shading. Compare whole-window ratings rather than only a center-of-glass value because the frame and edge details also affect performance.
A room's comfort also depends on air leakage, insulation, sun exposure, HVAC distribution and interior shading. Windows facing different directions may not benefit from the same solar-control approach. A visible light rating concerns daylight transmission, not insulation. Consider these trade-offs together rather than assuming one number selects the best window for every opening.
Gaps around the opening, poor perimeter sealing and unresolved water problems can undermine a high-performing product. Useful records include the NFRC label, product series and installation method. Existing windows sometimes benefit from compatible weatherstripping or other repairs, but water damage, unsafe glazing and failed operation need separate attention. No label guarantees a particular energy bill reduction.
Do not obstruct escape openings or drainage paths when adding coverings or seals. Energy savings depend on the entire home, climate and use; a product rating is not a guaranteed savings amount.
These references provide supporting guidance and further reading. Follow current local requirements and the instructions for your exact products; some publications address particular materials, products or code editions.