Boilers are fairly simple; they apply heat to water, which boils and circulates through the system in the form of very hot water or steam. Thermal energy moves from high to low temperatures, so heat is transferred from the water or steam to the air. Condensing boilers are box-like with the heat source and other components housed safely in a cast iron, copper, steel or stainless steel casing. Most boilers need to be in a fireproof and well-ventilated area with intakes for water and fuel. They provide hot air and water, two important parts of daily life.
Condensing boilers are found in industrial environments, offices, schools, residential units and many other buildings; they can also be used to heat pools, for example. Mobile boiler units are used in emergency and military situations for temporary heating. Condensing boilers also find uses beyond general heating. They provide hot water that is used in manufacturing and industrial processes.
Condensing boilers work the same way that conventional boilers do with one main difference. Fuels such as wood, coal or natural gas are burned, producing hot gasses that pass through a series of metal rods or tubes that are immersed in water. The heat from the gas is transferred to the metal rods and then to the water. The temperature of the water increases and the hot water can be used in a variety of ways. In a conventional boiler such as a combi boiler the water vapor would escape through the flue. Condensing boilers prevent this, trapping the steam and condensing it back into liquid water.
These boilers rely on their design for maximum success, usually by having large or dual heat exchangers (the metal rods and tubes). Condensing boilers offer efficiency levels of about 30% greater than conventional boilers as well as significantly fewer CO2 emissions. The temperature of gases leaving the flue in a conventional boiler are 120°F or more while condensing boilers release gases at temperatures of 50-60°F. There are three kinds of condensing boilers. Regular boilers have a hot water cylinder to store water while combination boilers do not; they use multiple heat sources to quickly heat water according to the demand. System boilers are also called sealed system boilers because they use hot water cylinders with most of the major components built in.