Gorell has also won numerous Energy Star awards. Regardless of your choice bear in mind that the window will be the weak point in a super insulated wall. A.20U equates to an R5 hole in an R40 wall. This is a big step. You will notice a difference when standing near the window. The installation also becomes very important so be sure choose a qualified installer. The area between the window frame and the adjoining wall must be properly flashed, sealed and insulated. Best of Luck

Actually it is a fiberglass exterior window with wood clad on the interior only. It is not a solid wood window wrapped with fiberglass ( not similar to a Marvin Premium....wood wrapped in extruded aluminum). Here is a link that might be useful: Integrity Image

Have you looked at Milgard? I looked at Anderson, Pella, Marvin, and Milgard, and my Milgards are finally getting installed TOMORROW! I was surprised how cheap triple glaze was to add, so I added it to all the windows, except one that was too big. I got the fiberglass. Triple glaze cost

My quote and specs are in Italian so ive used goodle translate. Im still not fluent! And i am trying to get pictures. "Good morning, as per your kind request, I am sending you the estimate of the Internorm model KF410 windows, they have the following generic characteristics: - 93mm frame with six chambers; - standard triple glass according to law with safety tempered glass (to avoid possible shocks thermal insulation) with perimeter glazing I-Tech glazing to ensure stability, thermal insulation and a exceptional safety; - black ISO glass spacer channel; - triple perimeter seal; - hidden hinges and satin chrome handles; - tilt and turn standard on windows and French windows; - color: internal wood effect film or pvc / external aluminum shell wood effect painted. POS.160: Lift and slide model KS430 - 200mm frame with six chambers; - triple glass with safety tempered glass (to avoid possible thermal shock) with gluing perimeter I-Tech glazing to guarantee stability, thermal insulation and exceptional safety; - black ISO glass spacer channel; - internal square G80 satin chrome handle and Dallas satin chrome external handle; - color: internal wood effect film or pvc / external aluminum shell wood effect painted" Example of a frame: 1 fixed door and 1 sliding: Frame width: 4500mm, Frame height: 2600mm, Div. In width: 2250/2250, Disassembled version, Frame: Normal frame, Lowered threshold, Fields: FIX / IF, Fixed element: IF door: Lifting door (HST) Left side: right, Item version: Transport depth / coupling: Without transport profile (-) Extras: Internal glass seal color: Black, Glass seal color ext .: Black, Pre-drilling for 3-sided screws (81) Altitude (a.s.l.) <700 m Transport: Logistic XL transport costs, The outer plate comes made of ESG-H instead of ESG., Edges of float glass sheets if> 1700 x 2500 mm, Uw (calculated on described finish, EN ISO 10077): 0.78 W / m²K