The zero drift, interference, and sensitivity of an HCl analyzer based on a non-dispersive infrared (NDIR) technique can be improved to develop a cost-effective solution for continuous emission monitoring systems (CEMSs). To achieve these improvements, the same bandpass filter technique, negligible interference bandpass filter, and optimal path length are applied to the analyzer. Laboratory inspections and long-term field trials are conducted to evaluate the performance of the analyzer. A metalworking factory and a cement factory are selected for field trials. In laboratory inspections, the relative error of the analyzer is less than 1%, aligning closely with the results obtained from standard ion chromatography methods. Moreover, the basic specifications of the proposed analyzer are comparable to those of commercial HCl analyzers. In field trials, the NDIR analyzer shows a significant bias compared to the standard method. However, when considering the difference between HCl emission levels and HCl emission standards, the relative errors are less than 10%. These results suggest the proposed NDIR analyzer is a practical option for the CEMS of metalworking and cement factories. However, seasonal variations should be considered when the temperatures of gas emissions are low.