This study deals with energy/exergy, exergy cost analyses and sustainability assessment of a low exergy heating system. In this study, an indoor sports hall with a volume of about 28,180 m(3) and a floor area of 2366 m(2) is considered as a case study. In this context, three different heating options are investigated, namely, (i) a conventional boiler, (ii) a condensing boiler and (iii) an air heat pump as driven by fuel-oil, natural gas and electricity, respectively. In this regard, an energy and exergy analysis is employed to assess their performances and compare them through energy and exergy efficiencies and sustainability index. Also, total exergy costs based on the considered systems with three different fuels are determined and compared with each other. Overall exergy efficiencies of the heating systems are found to be 2.10%, 2.33% and 2.42% while their corresponding sustainability index values of the analyzed cases are calculated to be 1.021, 1.024 and 1.025 for cases 1 through 3, respectively. Total exergy costs of the considered systems are obtained to be C-case1 > C-case3 > C-case2. Based on the exergy cost analysis results, the most cost effective system is Case 2. (C) 2012 Elsevier B.V. All rights reserved.