Share 'The Truth About Windows?'

I just had another window salesman knock on my door and tell me that switching out my windows can save me 40% to 50% on my energy bills. When I pressed him, he said that's for switching out metal double pane windows with his high efficiency triple pane ones here in Texas.  He promised much higher savings when it comes to switching out my single pane metal ones.   I've modeled a lot of buildings f…