In this study, the effect of additional solid surfaces that placed in the combustion chamber on the flame temperature and nitrogen oxide emissions was experimentally investigated. In order to increase the solid surface radiation in the combustion chamber, the wing was added to the solid surface. The solid radiation surface (named as "filling material") was stainless steel tube with a wall of thickness 1 mm and diameters of 25 and 30 cm with lengths of 20 cm. Filling materials with 2, 4, 6 wings were placed in the combustion chamber of a 116 kW fire tube water which is defined in the Turkish Standards TS EN 676, and the flame temperature and NOx emissions were measured in the combustion chamber. According to the experiments, it was seen that the as the number of wing increases on filling material with 30 cm diameter, temperature and NOx emissions in the flame back return region were decreased. The flue gas temperature and NOx emission of the flue gas leaving the boiler were measured lower than the no fill material case.