The paper deals with waste gasification as a technology allowing for indirect co-firing of large quantities of biodegradable wastes in coal-fired power boilers. In contrast to common landfilling and direct co-firing, gasification of wastes presents a number of advantages. Problematic species in original feedstocks can be partly safely incinerated in the furnace and partly retained in the gasification residues. The paper focuses on the impact of indirect co-firing on basic boiler parameters and performance. The work carried out was in the form of a case study for co-firing LCV gas in a 230t/h dual fuel pulverized coal-gas fired boiler. Thermal shares of 10, 20 and 40% have been investigated for two extreme LCV gas qualities represented in the calculations by its calorific value of 2.0 and 8.5 MJ/m(n)(3) respectively, thus six calculation cases are given. The results of the study reveal that even high thermal shares of LCV gas may be achieved for co-firing of better quality gas without significant effects on boiler operation. For lower quality gas, even a 10% thermal share influenced boiler operation to a great extent. This paper also gives consideration in relation to avoided CO2 emissions accomplished via indirect co-firing. (c) 2008 Elsevier Ltd. All rights reserved.