A flue gas heat recovery system includes a heat exchanger fluidly interposed between a furnace and a chimney to receive hot flue gas from the furnace. The heat exchanger is releasably mounted in the chimney and includes a partition which forces air being heated by the heat exchanger to traverse a path through the heat exchanger which maximizes the time of contact between that air and the heat exchanger heating elements. The partition further creates turbulence in the heat air.
