We use dual pane windows with low E glass. The heat loss and gain is minimal.

hamou,
One step towards an energy efficient home is your windows & doors.
All of our Renaissance solid bronze windows & doors come with triple seal glass and double weatherstripping, although we do not currently offer a thermally broken unit.
With the narrow profile of our bronze, the glass and weatherstripping can have a greater impact on the overall performance of the window.
All windows and doors are rated with a solar heat gain co-efficient (SHGC) and U-factor, so you could check those requirements to meet your needs. This link may be helpful to you http://www.milgard.com/energy-calculator/

You are welcome to view our ideabooks or product video & website-
http://www.houzz.com/ideabooks/27094077/thumbs/Black-Kitchen-Windows
http://www.houzz.com/projects/573835/The-von-Behr-Estate-in-Sisterdale--TX
http://www.houzz.com/projects/152134/Renaissance-Solid-Bronze-Windows---Doors-by-Progressive-Solutions
http://www.houzz.com/ideabooks/7715785/thumbs/Bronze--Copper---Steel-Door-Ideas

http://blog.werefindinganswers.com/gallery/renaissance-bronze-windows-doors-2

http://solidbronzewindows.com

in my country we still use wood in our windows or aluminium and no bronze

if i can use french as language it will be greater i am not good enough in engish