Chimney plays very important role in the exhaust of flue gases from boiler to the atmosphere. An initial design of chimney heat recovery heat exchanger was provided. The design had a completely fabricated exchange core but an incomplete ducting system .This report is based on the work undertaken to complete and test the gas to gas heat recovery system. This system will design specifically for boiler chimney and therefore the systems ducting will design to conform to the general boiler stack. In the completion of the design, the major factor to consider is to design against fouling. The system is therefore design with means of reducing fouling such as provision for easily replaceable particulate filter and quick washing system.