This paper presents three-dimensional study on the enhancement of waste heat recovery from vertical chimney via  thermoelectric generators (TEG) by using heat spreader. The physical model composes of aligned  TEGs mounted on the chimney wall where each TEG is cooled at its cold side by rectangular finned  heat  sink. The  spreaders are installed on the generators’ cold sides between the generators and the  heat sinks’ bases. The studied model represents three of the TEGs installed on the chimney wall. Three dimensional model is  presented for the physical model coupling the governing equations of thermal, fluid flow  and electrical models and is solved by using ANSYS software. Results indicate that using spreader increases  total  output  generators  power by 17% and 42% at spreader length 40 and 140 mm, respectively and  pitch 140 mm. The increase of the TEGs power is about 17% and 21% due to using spreader length
of 40  and 80 mm, respectively at 80 mm pitch. Using heat spreader with maximum length of 140 mm, increases  the conversion efficiency of the lower, middle generator and upper TEGs by 22.2%, 18.8%, and 19.7%,  respectively, while the overall efficiency of the system rises by 20.4%. Using spreader with 140 mm reduces  the used generators and heat sinks numbers to approximately the half.