; RavenWindowTM is quite simply the most energy-efficient window in the world.RavenWindowTM has a center-glass U value of 1.7 W/m2K (0.22 BTU/h-ft2-F), with a Solar Heat Gain Coefficient... in all four seasons. FeaturesSlash your energy bills by 30% or more*Double the energy savings of the leading energy-efficient window Adjusts automatically to maximize energy...RavenWindow Our Products >> RavenWindowRavenWindow Until now, windows have been part of the energy problem for architects, builders and building operators.Sunlight from windows...