This experimental investigation is aimed at studying the influence of five significant parameters, namely swirl flow, loading height, primary aeration, gas flow rate (heat input), gas supply pressure and semi-confined combustion flame on thermal efficiency and CO emissions of domestic gas burners. We focus particularly on the effects of a swirling flame on the performance of the new swirl flow burner (SB). The results shoved that the swirl flow burner (SB) yields higher thermal efficiency and emits only slightly higher CO concentration than those of the conventions: radial flow burner (RB). These characteristics are attributed to the significant improvement in heat transfer coefficient at the vessel bottom resulting from the prolonged residence time of the combustion products in the vicinity of the vessel bottom. With the increase of loading height, the CO emission decreases owing to the reduction of quenching by flame impingement on the load. However, at high loading height, the flame and combustion gases are cooled to a greater extent by mixing with ambient air before contacting the loading vessel, and thus, the temperature gradient for heat transfer is decreased, which leads to the decrease of thermal efficiency. As the thermal input increases, the thermal efficiency is reduced and the CO emission increases. With increasing primary aeration, the CO emission is diminished, but the thermal efficiency is almost unaffected. Additionally, the addition of a shield (named semi-confined combustion flame) achieves a great increase in thermal efficiency. The thermal efficiency of the SB with the semi-confined combustion flame yields a markedly higher thermal efficiency, by about 12%, than that of the RB with open flame. (C) 2006 Elsevier Ltd. All rights reserved.