A boiler gas flow distribution fin includes an elongated flow distribution fin protruding from a back wall of a flow distribution channel into a hot gas flow path from a boiler combustion chamber. The flow distribution fin can include a leading segment with a leading ridge, a medial segment with a medial ridge, and a trailing segment with a trailing ridge. A gap between the fin ridges and a set of convective fins in an adjacent flue passageway segment can vary from a larger gap at the leading ridge to a smaller gap at the trailing ridge, transitioning along the medial ridge. The flow distribution fin can aid in directing a hot gas flow from a combustion chamber into the flue passageway segment, resulting in a substantially balanced mass flow rate through each of a series of flue passageway sections.