What did you first notice on this photograph? If you are a sad individual like me, you noticed the condensation on the glass, which obstructs the view of the yellow wings and the black belly of the tit outside. This photo shows two environments inhabited by the tropical bird one one side, and the winter bird staring at each other, separated by the architectural glazing. A small miracle caused by the human intervention in the nature, and on the engineering side by the mechanical system delivering heat and the building envelope containing the heat. The glazed partition conducts heat well, which warms the bird on the exterior, but chills the bird on the interior at the same time. Water condenses on the cool interior surface of the glass, dehumidifying the air adjacent to the window. Such a condensation inside is one of the most common problems with building enclosures in a winter. It wouldn’t have happened if the window was specified correctly and verified by simulations or testing.