Biomass-fired boilers are widely recognized as a sustainable energy source, offering a renewable alternative to conventional fossil fuels. Despite their benefits, these systems often experience significant thermal losses, which can be mitigated through advanced waste heat recovery technologies. This study focuses on improving the energy efficiency of biomass-fired boilers by integrating a condensing heat exchanger (CHEX) to recover both latent and sensible heat from exhaust gases. An experimental study was conducted to evaluate the system’s efficiency with and without the CHEX under various operating conditions and with different exchanger configurations. A one-dimensional thermodynamic model of the system was developed using Ebsilon@Professional software to simulate the system’s behavior, validate the experimental results, and optimize key parameters. The findings highlight the viability of integrating waste heat recovery systems into biomass-fired boilers, emphasizing the importance of both experimental validation and advanced modeling in optimizing thermal systems. This research provides valuable insights for designing more efficient biomass energy solutions to meet global sustainability goals.