The article justifies the application of gas fuels for supplying auxiliary ship boilers. It presents legal regulations on maritime environmental protection areas and their requirements which are in power. It shows the chronology of introduced limitations on sulphur and nitrogen dioxide emissions and thresholds of carbon dioxide emission reduction expressed by EEDI (Energy Efficiency Design Indicator) and EEOI (Energy Efficiency Operational Indicator). Ways to decrease the values of EEDI and EEOI in the ship energy effectiveness management have been shown. Consequences of replacing marine fuels with LNG for running auxiliary ship boilers have been considered thoroughly, taking into account ecological, constructional, operational, procedural and logistic limitations as well as economic consequences. The summary shows the influence of particular consequences of using LNG for running boilers on the methods of maintenance of auxiliary boilers.