Existing Radiator System

I have a 2 story building with two apartments. There is hot water radiator heat.
One thermostat controls both units.
I need to know how a hot water radiator system is piped. I would like to separate the units to have two separate boilers.

Please only helpful answers.

Walter

No one here can tell you how your specific system is put together. Lots of folks know what the components are, how they are assembled, how they work, and how to troubleshoot them. No one can see your structure and system.

You'll just have to call a local contractor or two and get recomendations and bids to do the work. Depending on local market, boiler selection, and accessibility for new zone piping and venting I suspect you're looking at more than $10,000. Could be double that. You'll just have to have folks look at what you've actually got in place.

Now if you were an industrious type of person you'd trace out piping and sketch the system. Post the sketch along with some photos of the existing boiler space and maybe someone here would help you. Maybe.

zones

In almost all systems, you cannot just separate it into 2 zones without major piping revisions. First you have to separate the affected radiation from the original zone, then ensure that the circulation of the original zone has not been degraded or restore it if it was, then repipe the removed radiation as a new system with all its controls, plus rewire the boiler to allow 2 zone operation. I hope you do not intend this to be a DIY operation.