An in-depth heat transfer analysis of RDF-5 Gasification in a downdraft gasifier has been investigated. RDF-5 has been prepared from the reclaimed landfill from old dumpsite, in a cylindrical form with a density higher than 600 kg/m³ after densification by extrusion. It is a mixed composition between waste plastic (polyethylene) and paper with a ratio of 75:25 %-wt. A downdraft gasifier has an operational capacity about 25 kg of feedstock per batch and has an inside diameter of 20 cm. and 2 m. in length. 11 thermocouples type K has been installed along the vertical height of the reactor to measure the distribution temperatures in each gasification reaction zones. Air blown has been used as gasifying agent and injected at the oxidation zone of the gasifier's body with the varying flow rate of 12, 15 and 18 Nm³/hr, respectively. RDF has introduced together with charcoal at the same weight to act as additive and increase the fix carbon ratio to improve gasification process. The gasification process has last for about 1.5 hr in each experiment. Syngas including CO, H₂ and CH₄ that generated from the process has been measured in order to evaluate the performance of the gasification in term of heating value which could be used as a green and clean fuel. The temperature distribution along the height of the reactor from each experiment has been studied to classify the reaction zones including drying, pyrolysis, oxidation and reaction zones. The temperature in oxidation and reaction zones indicates the significant control parameter to govern the quality of syngas. The heat transfer mechanism by conduction, convection and radiation in each reaction zone has also analyzed and benefit to be used in operational planning and modeling.