I can tell you work on the commercial/industrial side of things
I work on commercial design, and I started as a plumbing designer.
I had to learn quick that "plumbers" deal with water, sewer pipes, compressed air, and for some reason natural gas. The "pipefitters" (we also called them "steamfitters", which may be wrong) were the ones that used black iron for just about everything. That included all of the piping for hot and chilled water for heating, fuel oil and diesel piping for generators and boilers, and then all of the steam and condensate lines.
In regards to the steam systems that put steam in the top and it comes out the bottom, those usually tend to be commercial steam coils or heat exchangers. They have the steam trap on them to regulate the flow of condensate that goes out, so they have to be located at the bottom of whatever equipment it is.