Restore 100-year-old radiators?

They surely can be restored. Furthermore, it is unlikely that any of the piping will have to be disturbed.

Stick with the steam -- since you have it, you will find that it is even, warm, cosy, comfortable, efficient, etc. etc You will find that the comfort of steam heat is very like radiant -- except for the warm floors, of course!

More specifically. It is rare for a radiator to be so damaged that it is unusable. Once in a very long time one may develop a leak -- but it is almost always between sections, and that is repairable quite easily. The valves and unions do sometimes leak -- but again, that is completely repairable (usually just with a nice wrench!). Some types of steam systems have traps. These may need replacing -- a simple job. Some have radiator vents. These may very likely need replacing; another simple job.

If they need refinishing -- which wouldn't surprise me -- there are a variety of ways to do that, ranging from really simple (wire brushing and painting) to pretty fancy (bead blasting and powder coating).

The boiler may or may not need replacing. If it is more than 15 years old, it probably does.

You state you want to replace all the plumbing. For the domestic water, perhaps. But may I ask why you want to replace the steam piping? I would approach that with a good deal of caution. While it certainly can be done, there should be a very good reason to do so -- and not because it is old. There may be a few pipes low down in the basement which are doubtful, but otherwise steam piping simply doesn't get old (the piping -- and radiators -- in the place I care for are over 80 years old, and in very very good condition, to give you the idea -- I expect them to last another century or so).

Give us some more information about your system, and we can probably help you further. You might also want to look into a couple of books: The Lost Art of Steam Heating and Greening Steam, both of which are available from the store on this site or from Amazon.

The steam piping in my house is 115 years old and many on this site have even older steam pipes. They will last almost indefinitely as long as the horizontals have proper pitch and there isn't a lot of fresh water added to the boiler, on a regular basis. About the only piping that will be suspect are any wet returns (pipes below the boiler water line) in the basement. When you have the boiler serviced, it would be a good idea to have those looked at and possible flushed out if there is access to open them up and clean out. If, when you have walls opened up or are inspecting the pipes in the basement, you see signs of rusty water runs on a pipe or around a fitting, that might be worth a closer look but I wouldn't replace all the steam pipes.