The BTG 20 LX it has two-stage progressive output operation. It has the ability to operate with output modulation by means of automatic RWF40 regulator mounted on the control panel (to be ordered separately with the modulation kit). It has air-gas mixing at blast-pipe with exhaust gas recycling blast-pipe able to achieve very low pollutant emissions. The product comes with regard to nitrous oxides The (NOx) and the ability to obtain optimal combustion with values by regulating combustion air and blast-pipe. The minimum and maximum air flow regulation for first and second stage by means of electric servomotor with pause closure of gate to prevent any heat dispersion to flue. A valve tightness control can be fitted on the burner.