Which property is most directly related to heat entering from the sun through glazing?

• A. SHGC
• B. U-value
• C. Fenestration
• D. Thermal mass

Answer: (A)

Solar Heat Gain Coefficient (SHGC) is the property that directly measures how much of the sun’s radiant energy actually becomes heat inside your space after passing through glazing. It’s the key factor for understanding cooling loads and how windows contribute to indoor heat. A lower SHGC means less solar heat enters, which is beneficial in hot climates or for rooms with strong sun exposure; you can achieve this with low‑E coatings, tinted glass, or multiple glazing layers.

U-value, on the other hand, tells you how well the window resists heat transfer due to temperature differences across it—essential for assessing heat loss or gain from conduction and convection, but it doesn’t quantify solar heat entering from the sun. Fenestration is the overall category of openings like windows and doors, not a single performance metric. Thermal mass describes how well materials store heat, influencing how quickly a space heats up or cools down, but it doesn’t determine how much solar heat passes through the glass.

So, the attribute that most directly relates to heat entering from the sun through glazing is SHGC.