Thermal Performance Rating 

H Window Company, LLC is a member of NFRC (National Fenestration Rating Council) and Energy Star.

NFRC-Total Unit U-Value ratings of 0.37 to 0.25 (Corresponding R-Values are 2.7 to 4.0) are determined by choice of glass and window configuration.  Better ratings can be obtained by use of special super-high-performance glass or interior removable glazing panels.