the difference between hot water and steam heat

That bullet shaped thing

is a thermostatic air vent, which closes when steam reaches it.

If there is only one pipe connected to the radiator, it's a "one-pipe" system, if there are two (with shutoff valves) it's a "two-pipe, air-vent" system.

Dan has written two great books on steam heating: "We Got Steam Heat!" and "The Lost Art of Steam Heating". The first is a beginning book for the home owner, the second goes into far more detail and is useful to the contractor as well as the home owner. You can order them on the Books and More page of this site.

The site also has a "Find a Professional" page, which is very useful when you need a contractor who knows steam.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Contractor"