In winter, minimizing heat loss via windows is primarily about reducing which characteristic?

• A. U-value
• B. SHGC
• C. Fenestration area
• D. Glass color

Answer: (A)

Heat loss through a window is governed by how easily heat can move through it, which is quantified by the U-value. A lower U-value means less heat transfers per square meter for each degree of temperature difference, so choosing windows with a low U-value reduces winter heat loss most effectively. SHGC matters for how much solar warmth can enter, which can offset heating needs, but the direct factor controlling heat loss is the U-value. Fenestration area affects total heat loss by size, and glass color has little impact on insulating performance.