The key feature of boilers is their ability to distribute heat generated via burning fuel throughout a structure. They typically do so by sending steam or hot water through pipes and radiators.
Boilers are popular options for heating homes. Most use natural gas, which is sent through a nozzle and lit on fire. This flame heats a container holding water. In older systems, the water was heated to generate steam, which expands automatically. Steam then flows through pipes to radiators, which warm the air around them to heat a room.
However, hot water boilers have become more popular over the years. Instead of heating the water until steam forms, they instead heat water and use pumps to send it to radiators. Since steam boilers must heat water more than hot water boilers, they lose a bit of efficiency in the process. Compared to furnaces and other heating options, however, steam boilers are still relatively efficient.
Newer boilers automate a number of functions to improve comfort and achieve better efficiency. Most boilers turn on when the temperature drops below a certain point and stop when the structure is heated. Boilers also contain pressure relief values that trigger when internal pressure is too high. Some boilers can even use different combustion processes to ensure smooth burn cycles, which provides superior efficiency.