Heating systems need air for combustion to take place. In open flue operation, the combustion air supply comes from gaps around windows or doors, or vents to the outside. However, because of the need to save energy, this uncontrolled flow of air in the living area is no longer in line with the latest engineering standards. Floorstanding boilers and wall mounted gas boilers can be operated in room sealed mode using advanced balanced flue systems. A concentric balanced flue enables considerable savings to be made on construction and installation costs.