I took this photo using a FLIR IR camera in January It was 17deg outside and if you look at my windows they are almost 40deg vs the surrounding house. The really interesting thing here is that the window on the right has an insulating shade in front of it so it is not nearly as warm on the outside. ie it is leaking less of my precious heat out of the house. Per some of your questions the windows are modern double pane Anderson windows>If you like this post check out this one on the US Department of Energy Solar Decathlon
Or this one Passive Solar water wall designs
