The energetic viability of a polyolefin pyrolysis unit that could be installed in a refinery plant was examined. Thermal pyrolysis at 500 and 700 degrees C, and the catalytic cracking by means of HZSM-5 and HY catalysts were analyzed. The energy requirements for an initial separation of the products by means of distillation towers into four main lumps (gas, gasoline fraction, diesel fraction, and waxes) that could be directly treated in a refinery were calculated as well. An energy balance closure and a sensitivity analysis were also carried out for all cases in order to check the accuracy of the yields of products previously obtained. These results were highly satisfactory for all cases, although the actual heat of combustion might be slightly higher than the values measured experimentally (around 5%). The results of the energetic viability analysis showed that only about 5% of the input mass flow rate is needed to burn to satisfy the energy requirements of the plant. Thus, the heat released in the combustion of the product fraction stream that is in minor proportion in each case proved to be sufficient.