Boilers are closed pressure vessels that were originally designed to heat water or other fluid. The heated or vaporized fluid in boilers today is not actually boiled, it exits the boiler for use in water heating, cooking, central heating, boiler-based power generation, and sanitation. The heating source in the boiler is typically a natural gas-fired burner.
Boilers provide radiant heat, which warms objects in a room. This type of heat is preferable because they people can set their thermostat at a lower temperature and the radiant heat makes the room feel warmer than the actual air temperature. Another advantage of this type of heat is that it feels like more balanced heat throughout the home, especially during the winter months.