I recently visited the Chapel at the Illinois Institute of Technology (IIT), designed by Ludwig Mies van der Rohe and completed in 1952. It is officially called the Robert F. Carr Memorial Chapel of St. Savior. Fun fact: even though it is a non-denominational chapel, it was paid for by the Episcopal Diocese of Chicago.
The air in the Chapel is not heated. In fact, there is no mechanical air system at all. The Chapel was (and is) heated by a hydronic (hot-water) radiant floor system. The floor is terrazzo. One can imagine that Mies preferred this system because it is invisible, and he did not need to worry about how ducts and diffusers would need to interact with the 'purity' of the structure and the architecture.
But there was one additional problem --- the cold-glass effect. To compensate, there are also a couple of radiators inside the glass. It's visually incongruent to see the Victorian method of radiator heating in such a quintessentially modern building. It must have been a painful compromise for Mies.
I am not sure how much insulation is (or was) in the brick walls, or the roof, or underneath the floor. Probably very little. Although the Chapel was restored in 2014 by Gunny Harboe the original mechanical systems weren't touched. As Blair Kamin noted, the chapel "can become an icebox during Chicago's brutally cold winters."
Also the chapel is oriented with the main glass facade to the east, and a secondary glass facade to the west. The entire south face is brick. Clearly Mies ignored the potential of passive solar heating. This may be considered a legacy of Zeilenbau orientation.