An experimental burner of the heat-recirculating-type was constructed and its thermal characteristics were investigated for methane-air fuel-lean combustion. Temperature distributions of air and burned gas flowing in the passes of the burner were determined by means of both experimental measurements and numerical simulations. Using the fractional heat recirculation rate as a criterion for thermal performance, the optimal design of the burner was examined in terms of a chemical parameter (the equivalence ratio), a fluid-mechanical parameter (the Reynolds number) and two geometrical parameters (the aspect ratio and the number of passes).