I stole this photo from the website of Fabrica718. It is an image taken with an infrared camera of a block of Brooklyn brownstones. The blue one is the one they remodelled….blue because its envelope is so well insulated that very little heat is escaping. Pretty cool. I’m not sure why most of the other houses have blue second and third story windows. I can’t imagine that the whole block has been upgraded to triple pane. Any ideas?