My current sliding glass doors are double pane with aluminum frame and original with the house which was built in 1985. This past winter we could really feel the cold air coming in (we live in Virginia). Will a new sliding glass door make a significant difference on electricity bills and comfort or should I just work on better insulating the doors? My other concern was how easily it could be lifted out by a burgalar, this could probably be remedied with an after market lock or some screws in the top of the frame. My contractor gave me a quote of about $2K to replace the current door with an Atrium brand door. Thoughts?