There is in existence no empirical equation for predicting the heat loss factor for a tubular absorber with a concentric glass cover, often employed as the target of a linear concentrator. A first attempt has been made to determine a solution for this geometry without the requirement of an iterative solution for the simultaneous equations. Our semi-empirical equation predicts the heat loss factor to within Â±1Â·2 per cent of the value obtained by the actual solution of the simultaneous equations, in the range of variables--wind velocity, 0Â·5 m/s to 10Â·0 m/s, absorber temperature, 20Â°C to 200Â°C above ambient air temperature and emittance of the black coating, 0Â·1 to 0Â·95. The proposed correlation also takes into account property variations. Also included is a comparison of the correlations used for computing the individual heat transfer coefficients.