In this study, the influence of fuel sources on entransy-based environmental impact and life cycle cost (LCC) analysis while determining the optimum insulation thickness (OIT) has been investigated. Analyses are carried out for the province of Istanbul, Turkey, considering energy demand in the heating period. Hydrogen, methanol, ethanol, natural gas, diesel fuel, and lignite are chosen as fuel sources, while glasswool is selected as the insulation material. The environmental and economic OIT, the total environmental impact and net environmental savings, the entransy loss and net savings in entransy, fuel consumption, CO2 emissions, fuel costs, insulation costs, total costs, and net savings in entransy costs are evaluated. The optimum environmental and economic glasswool insulation thicknesses are calculated to be: i) for hydrogen 0.297 m and 0.0855m, ii) for methanol 0.211 m and 0.0044m, iii) for ethanol 0.226 m and 0.0419m, iv) for natural gas 0.126 m and 0.0026 m, v) for diesel 0.185 m and 0.0287 m, vi) and for lignite 0.138 m and 0.0230 m. According to the environmental and economic evaluation made in this study, it is understood that natural gas comes to the fore and that our domestic lignite resources can be an alternative to this. In addition, in order to reduce the environmental impact factor of hydrogen, which is a pure carbon-free fuel, green and low-cost hydrogen production methods should be preferred.