"Ray" wrote in message
news:foj%g.2206$%T3.919@trndny03...
Our building plumber told me that the on-off valves on steam radiators
should be either turned on or off. He said they are not like a
water-faucet which can regulate the stream, but are like light switches
which are either on or off.

Is this accurate?

Pretty much. While you can regulate steam flow with a valve, it is not
easily done for your use and can also cause pre-mature failure of the valve
seats.

Depending on your system, you are running from a half pound to maybe 5
pounds of steam pressure. to regulate the flow to lower the temperature of
a given radiator takes a rather small orifice. Once it passes though the
orifice, it will expand to fill the entire space to give off the heat energy
it carries.

Steam, since it contains water vapor, is very erosive and will cut grooves
into metal, glass, whatever it is passing through.

One reason steam is used to heat large buildings is the ability to pack a
lot of energy in a small space compared to water. It can be moved
efficiently long distances from the boiler to the point of use. This is
especially true of high pressure steam.