"Ray" wrote in message
news:f5G%i.81$Jy1.25@trndny02...
For obvious reasons, we are thinking of switching from oil to natural gas
to fire the furnace for our steam radiator system in a six-unit coop
apartment building.

The furnace is fairly new. The question is, would we have to replace the
entire furnace, or could we simply convert the existing one for use with
gas?

Depends. First of all, you don't have a furnace. Furnaces heat air. Boilers
heat water or make steam. Since you state you have steam heat, it is safe
to assume you have a boiler.

Boilers consists of two main sections. The burner and the heating chamber.
Most can be had from the factory with a choice of fuels or even dual fueled.
There is a very good chance you can convert to gas simply by changing
burners, installing the proper piping for the gas, then remove the oil tank.

For more details and cost estimates, call you boiler dealer.