Each boiler variety is well suited to some applications and less well suited to others. For example, a wood fired boiler is an excellent choice when installation cost is not an issue and when an ample supply of wood is available for burning. In other cases, natural gas is the most practical fuel; in homes that were originally built with gas furnaces, it can be less expensive to improve existing ductwork as well as windows and door seals that it can be to replace an entire system with a new boiler that features a different heat generation method. Because boilers vary so widely in terms of their cost at installation and their lifelong maintenance costs, it is impossible to say whether one configuration is always more efficient or economical than another; those factors vary depending on the situation.
As far as residential and commercial heating are concerned, there are two main types of boilers: those that actually boil water and those that merely heat it. Boilers used to boil water can be used to heat buildings and to generate steam that can be harnessed and used in the performance of mechanical work by a machine. When such a boiler heats water to its boiling point, the steam produced is captured in a tank and is compressed there. When the steam in the vessel is sufficiently compressed, it is released through a valve. If the steam is being used to heat a building, it is distributed to radiators or other heat exchanging equipment that releases the heat from the steam into the air. If the steam is being used by equipment to produce work, it is forced into the machinery in whatever way is appropriate.
Electric heaters are sometimes used for both purposes. In homes and businesses, electric boilers are prized because they are easier to clean than gas fired boilers. They can also be safer, as no carbon monoxide or other combustion byproducts are produced by electric boilers. In the case of water heating, more recent developments in electric water heater technology has allowed for more rapid heating and more consistent temperatures.