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Nevertheless, given the fact that the burning equipment design and natural gas composition from the national grid is not significantly different from European countries, the outcomes represent an important landmark. By adding up to 30% of H\({}_{2}\) by volume, the authors did not experience flashback, flame lift, or CO emissions above 400 ppm. Another conclusion was that the efficiency of the appliances tested only varied by 1-1.5% with 0 to 30% hydrogen added to the mixture. Although this paper has an important experimental part, the burners tested are an atmospheric type and are not suitable for condensing boilers, which makes the separate theoretical and experimental analysis of burning equipment involving the condensation of water vapor in the flue gas the most important. THyGA Project, carried out by [PERSON] et al. [6], was one of the most complex projects involving the testing of numerous pieces of combustion equipment on the impact of a hydrogen-natural gas mixture on the performance and emissions. The project members tested gas boilers, room sealed boilers, gas engines, gas turbines, heat pumps, ovens, and fryers, in order to highlight what functional changes occur when replacing natural gas with a mixture containing a percentage of hydrogen. Nonetheless, the experimental results, in terms of condensing boilers, are extremely limited, and thus there is a need for experimental and theoretical research to cover this lack of information. One of the project's main conclusions was that the burning equipment behavior at high hydrogen participation in combustibles can vary substantially, depending on the system (for example, premixed or non-premixed system). A thermal power decrease of up to a maximum of 12% at 30 vol.% hydrogen admixture, compared to the operation with natural gas, was noted. Regarding CO and NO\({}_{\mathrm{x}}\) emissions, as well as flame temperature, different results were obtained. In some cases, the concentrations increased; in other cases, decreases were reported. As a direct result, further research is necessary in order to have a clearer and more complete overview on the process. [PERSON], [PERSON] et al. [7] have evaluated the burning appliance and equipment performance fed by hydrogen-enriched natural gas. There were reported no major operable problems and thermal power and CO2 emissions decreased with increasing hydrogen content. CO and NOx have not exceeded the permitted limits. The effect of hydrogen admixture on possible flashbacks, burning velocities and thermal performances related to domestic appliance was investigated by [PERSON] et al. in [8]. The main conclusion was that 20% hydrogen admixture in comparison with pure methane reduces thermal power by 4.7%, and the end users of the appliance must be aware of this loss, bearing in mind to maximize the decarbonization. [PERSON] et al. [9] conducted a theoretical study in order to determine the effects of hydrogen-enriched methane combustion on latent heat recovery potential and on environmental impact of condensing boilers. For this purpose, the authors used the Ostwald diagram. The authors emphasized the potential rise of NOx emissions with the increasing H2 participation in the mixture, which is induced by the increase in the adiabatic flame temperature. At the same time, a CO2 reduction by 56.15% was found together with an increase in the air excess ratio with 0.1. Research has also been conducted on the performance of hydrogen-enriched methane combustion in a furnace, by [PERSON] et al. [10]. The authors conducted a CFD numerical simulation of a furnace and concluded that the variation in the injector's geometry has no significant impact on equipment functionality in the case of high H2 contents in the mixture. Evaluation on combustion of hydrogen/natural gas blends in a compression ignition engine has been made by [PERSON] et al. [11]. This theoretical study demonstrates that H2 enrichment accelerates the combustion process and promotes its completion, strongly decreasing CO emissions.