One-Pipe or Two-Pipe Steam RadiatorsIn the one pipe radiator system, a single pipe runs from the furnace to each radiator. Steam is driven through that pipe, fills the radiators, and then condenses and runs back down that same pipe in the form of water. The water is recycled and used again in the next cycle.
In the two pipe radiator system, one pipe delivers steam to the radiators and a second pipe separately returns condensed water back to the furnace.
Steam Radiators: Any Good?Radiators are a very efficient, cost-saving way of heating a house. Even after the furnace has finished its cycle and heated a room to its thermostatically controlled temperature, the radiator continues to emanate heat. Even delivery pipes are a source of heat--spreading out the heating over a wide area.
Steam radiators can be messy. Many older homes with steam radiators have warped floors around the radiator area, an almost unavoidable byproduct of having a pressurized steam unit inside your house. Furnaces generating steam do so under pressure, and it is possible for these furnaces to explode.
Finally, a house with steam radiators is never a quiet house. While you can take measures to mitigate the sounds, you will always experience some degree of clanking (of pipes) and hissing (of steam escaping from valves). This is usually considered the price--or benefit--of living in an old home, whatever your view on the matter.