Steam boilers are among the most efficient central heating options, but hot water boilers are slightly more efficient. However, older steam boilers, which are still widely used, are far less efficient than newer units.
Boilers burn a fuel to heat water that is then distributed through pipes and radiators to heat a structure. Steam boilers convert water into steam, which expands and flows through the system automatically. Hot water boilers, on the other hand, distribute heated water using pumps.
The higher operating temperature of steam boilers leads to some unavoidable inefficiency since the hot water cannot be distributed through the system until it's converted into steam. Their ability to function without pumps, however, made steam boilers popular in the past, when pumps were less reliable. Despite the better efficiency of hot water boilers, converting the pipes and radiators to use hot water instead of steam can be expensive. Because of this, a new steam boiler may be a better purchase.
Natural gas is the most popular fuel for boilers, and its low cost, stable pricing and efficient operation makes natural gas the top choice where it's available. Oil is still popular in some regions, and those who do not have access to a gas line may prefer storing oil containers over compressed gas tanks.