In the present study, chemiluminescence analysis is used to determine the optimum range for equivalence ratio (Phi) in a multi-hole cylindrical burner. The premixed burner which uses natural gas is widely applied in gas condensing boilers and is examined here by Flame Emission Spectroscopy (FES). A spectrometry setup was implemented to capture emission of the burner, in order to detect OH', CH', C2*, and CO2* species by their chemiluminescence. The emission of OW and CO2* was investigated for different equivalence ratios and burner power showing a peak in the lean ranges of (1)= 0.77-0.85 and 0.78-0.85 respectively, that corresponds to the maximum heat release rate. In addition, the OH'/CH' intensity ratio was investigated for range of (1) = 0.6-1.2 for all burner power, resulting in a power independent relation for OH*/CW. It can be used as a tool to derive equivalence ratio from the OW/CH* ratio. Moreover, the maximum surface temperature of the burner in power range occurred at it = 0.82 in a promising agreement with chemiluminescence peaks of OH' and CO2". The main contribution is to find the optimum range of equivalence ratio corresponding to the maximum heat release rate. (C) 2019 Elsevier Ltd. All rights reserved.