My house was built in the 1920s, the heating source was a hot water/radiator system. Originally the basement was probably used only for a coal furnace (we have the drop-off door that the coal guy used to deliver through). We are looking at putting the basement to use and one of the major issues is the presence of 2" pipes for supply and return to/from the now-gas furnace. The supply and the return are not the same pipe. These pipes drop down from the ceiling and slope towards the furnace. Because these pipes aren't running through the joist bays and because of their downward slope, they can be as low as 6' from the basement floor surface.
The pipes are probably steel or cast iron (they're really thick, so unlikely to be copper).
I'm wondering if anyone has replaced their basement hydronic piping with something like PEX, and if so what was the required slope back to the boiler?
Edit: Based on comments from @SteveSh the slope was probably due to this system being steam originally. It must have been retrofitted a while back to use hot water instead. The slope is now not as important, but I'm still interested in hearing if people have replaced their hot water pipes with PEX. Any challenges that come up with that type of work?