NFRC
NFRC (National Fenestration Rating Council) is a non-profit organization that administers the only uniform, independent rating system for the energy performance of windows, doors, and skylights.
The NFRC program gives homeowners a resource to make educated decisions regarding the purchase of these home improvement products.
Energy Star
Energy Star ratings for thermal efficiency of home products help guide you to the best performing window and door replacement solutions.
Thanks to advances in technology, today’s ENERGY STAR certified windows, doors, and skylights offer greater savings than ever before. Just look for the ENERGY STAR label.
Efficient Windows Collaborative
This site provides unbiased information on the benefits of energy-efficient windows, how they work, and recommendations for their selection and use.
They offer a window selection tool, design guidance and more.