The nitriding efficiency of a low pressure r.f. plasma is investigated in an industrial style hot-wall furnace in which the component is heated by thermal radiation from the walls of the vacuum chamber. The role of degassed impurities is also addressed. Samples of AISI 316 stainless steel were treated at a relatively low temperature of 400 degrees C to avoid loss of corrosion resistance. The results are compared with treatments under similar conditions of plasma (sample bias, gas pressure, process temperature and treatment time), in cold wall experimental reactors, including a fully UHV compatible apparatus. Process conditions can be found for which the hot-wall furnace gives the best results, despite a high rate of impurity evolution. The apparently higher activity of the low pressure r.f. plasma in this environment can be exploited for low temperature plasma assisted nitriding.