Boiler systems work well in large buildings with many rooms, which is why they are used in many apartment buildings. Hot water is circulated throughout the building from a large boiler in the basement through a series of pipes. This process would be more difficult with a forced air furnace because of the size of the vents and because the air would have cooled by the time it reached the upper floors. Boiler systems can be easily scaled to suit the size of the building that they are heating.
Because boiler systems heat rooms using closed loops, they don't create dust in the same way that forced air furnace systems do. This dust is a problem for people with allergies or sensitivities and isn't particularly healthy for anyone. The heat in a boiler system radiates out from the radiator into the air that's already in the room; thus new air isn't introduced, and the air isn't moving as in a forced air system. The lack of new air and lack of blowing air both eliminate dust problems.
Radiators distribute heat throughout a living space in an even way that helps to eliminate drafts. Although they don't necessarily make a room warmer than other forms of heating, the feel of the heat is different because it is infusing the air rather than being introduced through a vent, which creates a comfortable feeling in the room.
Boiler systems can be easily built with separate zones that can be turned on and off, allowing homeowners to heat some parts of a house and not others or to heat different zones to different temperatures.
The little noise that a boiler heating system produces is confined to the burning of the gas or other fuel that heats the water in the boiler. With the exception of occasional clanking pipes in older systems, the rest of the system is completely silent. Forced air systems are disturbing to some people because of the noise of the circulating air.