A gasifier system for converting biomass to biogas includes a reaction chamber with a biomass supply port for receiving a biomass volume, a waste outlet port for discharging biomass conversion by-products, a gas inlet for receiving heated oxidizing gas, a gas outlet for discharging generated biogas and a burner manifold for distributing oxidizing gas within the chamber to react the biomass. The burner manifold includes primary tubes and secondary tubes, positioned in a vertically lower part of the chamber and configured with multiple openings or ports for dispensing the oxidizing gas, where the secondary tubes extend into, inject and evenly distribute the oxidizing gas into the biomass volume to optimize conversion to biogas.