This study investigates the thermal and hydraulic behavior of a thermal oil heater integrated into an Organic Rankine Cycle (ORC)-based waste-to-energy system, focusing on the influence of inlet air and oil mass flow rates on heat transfer and pressure drop characteristics. A series of computational fluid dynamics (CFD) simulations were conducted to analyze temperature distribution, flow dynamics, and pressure variations under varying flow conditions. The results show that increasing the inlet air mass flow rate from 0.3 kg/s to 1.3 kg/s significantly enhances convective heat transfer, raising the oil outlet temperature from 333.99 K to 385.99 K. However, higher oil mass flow rates tend to reduce this temperature gain due to shorter residence times. Statistical analysis (ANOVA) confirms the dominant influence of air flow rate on outlet air temperature (F = 233.892, η² = 0.985) and the significant effect of oil flow rate on oil outlet temperature (F = 10.164, η² = 0.604). Additionally, pressure drop analysis reveals that increased air flow rates lead to greater turbulence and higher resistance, with pressure loss rising from 85.3 Pa to 1648.5 Pa, while oil-side pressure drop remains relatively stable. These variations indicate a clear trade-off between flow conditions and system stability. Economically, higher flow configurations drastically raise operational costs, with annual energy consumption rising from IDR 133,331 to IDR 8,936,157 due to increased blower and pump power requirements. This study provides critical insights into the thermal-fluid interaction and economic implications of operating parameter variations, offering a foundation for optimizing thermal oil heater designs in ORC-based waste heat recovery systems