Replacement windows and doors have improved a lot. Modern products include many energy-saving upgrades. Today, whole window performance measures how much energy a window saves after installation. If you plan to replace your windows, learn the key metrics. Prestige Windows & Doors, a local leader, can help you interpret them.
1. U-Factor
U-factor describes a window’s insulation performance. It measures the rate of heat loss through the entire window assembly. The lower the U-factor, the better the window resists heat flow. For example, many double-pane windows now have a U-factor of 0.30 or lower. If you live in a warm climate, choose a low U-factor to reduce cooling loads.
2. Solar Heat Gain Coefficient (SHGC)
The Solar Heat Gain Coefficient, or SHGC, shows how much solar heat a window transmits. It ranges from 0 to 1. A lower SHGC means the window transmits less solar heat. This can reduce cooling costs in summer. However, solar heat can help heat a building in winter. Because of that, balance SHGC with local climate and building design needs.
3. Air Leakage (AL)
Air leakage measures how much outside air passes through cracks in the window assembly. The metric uses cubic feet of air per square foot of window area. A lower AL rating means fewer drafts and better overall performance. For ENERGY STAR certification, windows typically need an AL of 0.30 or less. Proper installation also matters because gaps and poor sealing increase leakage.
How these metrics work together
No single metric tells the whole story. For example, a window with a low U-factor but high SHGC might perform poorly in very sunny climates. Conversely, a low SHGC and poor air sealing can still let unwanted heat transfer occur. Because of this, compare U-factor, SHGC, and AL together. Consider the orientation of each window, the local climate, and the building use.
Choosing the right window for your property
Start by identifying your goals. Do you want lower cooling bills, more winter heat gain, or improved comfort? Next, compare certified ratings from trusted manufacturers. Finally, factor in installation quality. Proper installation ensures the window meets its rated performance because even a great product underperforms if it is poorly installed.
Call to Action
Contact Prestige Windows & Doors to discuss whole window performance. We install residential and commercial windows and storefront doors. Call us at (866)-466-5094 or fill out our online form to request an estimate. Our team will evaluate your needs and recommend the best options.