Carbon monoxide is often produced during the incomplete combustion of volatile organic carbon compounds in industry. In the combustion chamber for oxidizing carbon monoxide emissions, a penta-coaxial port device can be used to improve the process of mixing the fuel and oxidizer. In this study, the conjugate heat transfer analysis was conducted by solving both Reynolds-averaged Navier–Stokes equations with the eddy dissipation model and solid heat conduction equation in the wall using Fluent 2019R2 to simulate the reaction flow of a volatile organic carbon compound burner and heat transfer of the stack insulation layer. The mass fractions of the O2, CO2, and CO gases; the temperature; and the velocity distribution in a combustion chamber were computed to investigate how various design parameters of the combustor, including air inlet size and stack height, and air inflow conditions affected the combustion performance. Results show that the size of the air inlet had only a minor effect on combustion efficiency and that the airstream forced by a fan significantly enhanced the combustion performance. In particular, increasing the height of the stack from 2 m to 4 m greatly increased combustion efficiency from 63% to 94%, with a 50% increase in the incoming air flow rate by natural convection, which demonstrates the importance of stack height in combustor design.