There is more to a Dual Pane window that its having two layers of glass. I have never seen the specs on the dual pane windows in the Montana.
Note:
When there is a difference between inside and outside temperatures, heat transfers through a window. It's lost to the outside during the heating season and is gained from the outside during the cooling season.
A window's thermal performance - which can be measured at the center of glass, the edge of glass and the frame - is rated with a U-value, its overall ability to resist heat flow.
Have you ever tried to drink hot coffee from a drinking glass? If so, you know that glass is a very good heat conductor. The outside of the container can quickly become too hot to hold. Using two layers of glass with an air space between - the idea behind the Thermos bottle, incidentally - dramatically cuts the heat flow.
Single-pane windows can act like that drinking glass, conducting heat to the outside. Dual-pane windows, with a 1/2 inch to 3/4 inch air space between sheets of glass, work like a Thermos bottle to cut down the flow of heat. If you replace the air between the panes with an inert gas like carbon dioxide, argon or krypton, the window will transfer even less heat and be even more efficient.
Is there 1/2 inch to 3/4 inches between the panes.. What is the "U factor" Are they gas filled????
The term "dual pane safety glass windows" means little..
Also
http://www.taunton.com/finehomebuild...ges/h00029.asp