Absorbed heat duty of process side of a fired heater often requires rigorous vapor-liquid equilibrium calculations and is usually performed with costly process simulator software. An alternative, shortcut method is proposed, which may be easily and efficiently implemented in a spreadsheet. The results of the proposed procedure were checked against those of a process simulator and against the results of the indirect efficiency calculation method, for three different existing refinery furnaces. The accuracy of the proposed method was found comparable to both the others. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.