A gas boiler is a piece of equipment that uses heat generated from the combustion of gas to heat water for domestic or commercial use. A boiler can be used to supply a building with either hot water or steam for the purposes of heating.
A boiler is generally fitted with a distribution system made of pipes, baseboard radiators and radiant floor systems. Gas boilers that are used to generate steam are capable of reaching higher operational temperatures but have a lower energy-efficiency rating. Energy efficiency in both gas- and electric-powered boilers is measured using a rating called the Annual Fuel Utilization Efficiency.