A turbulent post-aerated town gas flame in a vertical water cooled tube of six inches internal diameter has been studied, with special reference to the radiation properties of the system. it was found that this system could be represented by dimensionless groups with a standard deviation of +/- 15%. It has been possible to correlate the apparent mean emissivity of the flame as an exponential function of the tube diameter and the air/gas ratio only, with a standard deviation of +/- 18%. Thence, by assuming a tempera ture distribution along the flame of a similar system in a three inch diameter tube, it was possible to predict the radiant heat transfer with a standard deviation of +/- 20%.