Abstract: A heat exchanger for a boiler comprises a central chamber for receiving a combustion gas. A baffle divides the central chamber into a first section and a second section. The baffle also restricts the combustion gas from flowing directly from the first section of the central chamber to the second section of the central chamber. There is a plurality of spaced-apart flues disposed about a periphery of the central chamber. The flues allow for communication between the first section of the central chamber and the second section of the central chamber, in particular, the flues allow for combustion gas to flow from the first section of the central chamber to the second sections of the central chamber.