Abstract: In a boiler, particularly a recirculating fluidized bed boiler, the tubes of heat exchanger banks (panels) are connected together so that they are securely supported against sideways movement. A first heat transfer panel has a first plurality of elongated heat transfer tubes, vertically stacked one atop the other, and extending horizontally in a first dimension; and a second heat transfer panel has a second plurality of vertically stacked heat transfer tubes extending horizontally in a second dimension, perpendicular to the first dimension. The panels are supported by walls of the boiler reaction chamber. Connectors attach one of the tubes of the second bank to the first bank to stiffen the first bank against sideways movement. The connectors may be bollard or triangularly shaped lugs welded to or operatively engaging tubes of both banks, or a tube of the first bank may be bent to form a loop, with a tube of the second bank passing through the loop and engaging the bends of the bent tube.