Biogas is deemed to be one of the most promising renewable fuels to have emerged in the past several decades. At present, biogas is mainly applied to cooking as a substitute for fossil fuels. Biogas is rarely reported to be used for space heating. In this paper, we describe a new design of biogas-fired partially premixed burner for a gas-fired wall-mounted boiler, which has a heat input of 25 kW and can be used for spacing heating and fermentation tank heating. 60% of CH4 and 40% of CO2 was the reference gas, and the jet diameter and burner port area were designed as 2.0mm and 4744.5mm² respectively, according to the calculation. Then, experiments were conducted to study the performance of the burner. Jet diameters were modified in order to investigate their effects on heat input, primary air ratio and flame stability of the burner. The results indicated that the burner showed superior performance when the jet diameter was set to 2.0 mm whilst the primary air ratio (α’) satisfied the design requirement. Moreover, the experiments of the gas-fired wall-mounted boiler were performed to explore the influence of different biogas compositions on exhaust emissions and thermal efficiency when this burner was installed inside. It was concluded that the content of CO met the national standard when methane content varied from 40% to 60%. However, with the increase of methane content, the thermal efficiency of the gas-fired wall-mounted boiler reduced greatly.