A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications. Heating boilers have many applications. They can be used stationary applications to provide heat, hot water, or steam for domestic use, or in generators and they can be used in mobile applications to provide steam for locomotion in applications such as trains, ships and boats. Using a boiler is a way to transfer stored energy from the fuel source to the water in the boiler, and then finally to point end use.
Water heating uses a combi boiler or a combination boiler which combines the chip heater with the domestic hot water in one box. They are not merely infinitively continuous water heaters having the ability to heat a hydronic heating system in a large house. When the domestic hot water is run off, the combi stops pumping water to the hydronic circuit and diverts all the boilers power to instantly heating domestic hot water. High flow rate combi boilers can simultaneously supply two showers.
The source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil or natural gas. Electric steam boiler uses resistance or immersion-type heating elements. Nuclear fission is also used as a heat source for generating steam. Heat recovery steam generators use the heat rejected from other processes such as gas turbines. Gas boilers or gas fired boiler heats, usually water, by using gas instead of wood or coal. An oil boiler uses oil or kerosene to heat.
A condensing boiler is a water heating device designed to recover energy normally discharged to the atmosphere through the flue. It can do this through the use of a secondary heat exchanger which most commonly uses residual heat in the flue gas to the heat cooler returning water stream or by having primary heat exchanger with sufficient surface for condensing to easily take place. The best term for condensing boilers on the primary heat exchanger may be fully condensing. A gas boiler remains the most popular type in North America.
