Dividing old hydronic system

rlaggren

The situation: We have an old (100year) house with two flats near Chicago. Heating was gravity hot water retrofitted with a gas boiler and circulator sometime in 1960's. Works OK mostly. We'd like to split the heating system into two when the time comes to do major work, eg. a new boiler; this would allow allow separate billing. There about about 20 cast iron radiators, 10 on each floor which are fine, more or less. A few were removed in the distant past and some are levitating at one end cuz of major settling over the past 60 years; no leaks or other issues, though. Pipes in the rough basement used to have insulation, now it's gone or crumbling; have to deal with some asbestous  there and insulate properly but it doesn't cause heating problems. There are two main loops in the basement.



The Plan: Disconnect all 1" risers and returns to either the first or second floor at their tees on the main loops. Either cap or connect each set of radiator supply stubs; I (really) hope not to cut into the old 2-1/2" (or 3"?) main pipes. Run new mains and connect (previously disconnected) existing risers to it. Sorry, I'm not at the house right now but I _think_ the existing system is a single pipe main (2 loops);  IAC, the concept is the same.



Obvious issues include not allowing old risers to drop into the basement when they're disconnected, removing asbestus, insulating properly, installing appropriate new boilers, allowing for zone controls in the future, isolating old from new pipe if new stuff is done in copper (first choice is black; need cast fittings or is steel OK?), installing mod/cons so I can poke the flu's out the side wall. Don't know about DHW heat at the moment but that piping would need splitting also. The space and the access is OK.



Main Q is whether removing half the riser/returns will make the original main loops disfunctional for some reason. Leaving the old mains will make that system mass a lot more than the new one but any reason it wouldn't work with the right pumps/controls?



Large amount of work, I know. This it still TBD, but the reasons to split it up are significant.



Thanks for any thoughts.



 Rufus