replacement window rating

Retrofit or replacement window costscommonly range from $5 to $50 per square foot of window Area. Some of the energy and comfort problems windows cause are inherent in their function as portals and lightsources. Window replacements or retrofits for energy efficiency must be designed to significantly reduce thermal transmittance, reduce solar transmittance, or reduce both.Thermal transmittance is measured by U-value and solar transmittance is measured bya number of factors discussed later. Air leakage reduction is usually a secondary benefit producing only small energy savings, unless the window has large visible air leaks.Doors generally have a higher thermal transmittance than walls, but a lower one than windows. Their surface Area is small and replacement cost is high, so door replacement is not usually considered a cost-effective energy conservation measure.However, doors can be a significant air leakage problem due to faulty operation or poor air seals.

Window research, testing, and rating. Four organizations serve as gate keepers for information about window thermal characteristics. Their roles are briefly explained here to facilitate further information gathering since this field is rapidly changing. National Fenestration Rating Council (NFRC): A public/private collaborative agency created to establish standardized window testing and rating. The Council simulates window performance with computers, then verifies simulation with laboratory testing. NFRC labels windows manufactured by members with various energy ratings. American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE): A professional society providing the theoretical framework for calculating heat flows through windows. ASHRAE's Handbook of the Fundamentals is the most complete common technical reference about window heatflows.Lawrence Berkeley Laboratory (LBL): North America's most authoritative and prolific window research facility, and experts in computer simulation of window heat flows. LBL researches and develops new window technologies and distributes information about windows. American Society for Testing and Materials (ASTM): Develops testing methodology for all types of building systems. Testing methods are specified by building codes and rating organizations like the NFRC.