Wood fiber is a great potential supportive material for creating a new composite the phase change materials (PCM) due to its beneficial qualities, including high sorption competency, low density, enviro -friendliness, economic effectiveness, and chemical inertness. The main objective of this paper is to study the effect of using the wood fiber/eutectic mixture of stearic and capric acid on the fuel, cost, and carbon emission-saving potentials for various PCM cases. Which experiences a phase transition within the thermally pleasant temperature range of buildings, used for the building's thermal energy storing purposes and consumption cost saving. The energy performance analysis was carried out for buildings incorporated with stearic and capric acid eutectic mixture of PCM with wood fiber-based insulation material (INS) in different climate regions. The results showed that the largest energy-saving capacity belongs to PCM5. The energy saving reaches 52.7% for PCM5 for a thickness of 0.1 m. The PCM1, PCM2, PCM3, PCM4 can provide energy saving rates of 23.5%, 34.3%, 44.7% and 50.5%, respectively. INS-PCM5 can provide about 1.74-, 1.5-, and 1.33 times larger cost savings than INS in 2nd, 3rd, and 4th regions for all fuels. The payback period varies between 0.37 and 5.81 years regarding the fuel and Region. Finally, the results indicate that the proposed composite provided a promising energy-saving potential in building applications by reducing.