In the present study, an experiment was conducted to investigate the heat and mass transfer performance of heat exchangers used in the condensing gas boiler. Two types of spiral circular fin-tube heat exchangers and a plain tube were tested in the flue gas of propane and dry air. Heat and mass transfer coefficients were measured and compared with the previous correlations. The experimental data for the sensible heat transfer of the plain tube reasonably agreed with the previous correlations for dry air and flue gas. However, the mass transfer coefficient of the plain tube was greater than the previous correlations. The pH, $NO_x$, and $SO_x$ data of condensate were provided.