This work determined the optimal locations for biomethane injection, from Centralised Anaerobic Digestion (CAD) facilities processing wastes, into the Irish gas network. The effects of incentives and plant size on; the sites selected, biomethane production, and feedstock utilisation, were assessed while maximising plant profitability. The first facilities to be constructed process household organic waste and were located in regions where this resource was highest. The number of viable facilities was dependent on the available incentives and ranged from 6 plants producing 0.53% of final Irish thermal energy use, to 22 plants producing 1.8% of final thermal energy use. The model proposed two facilities that processed household organic waste at a maximum size of 200 GWh/a or 6 at a maximum size of 50 GWh/a. Increasing maximum allowable plant size reduced the overall total number of viable plants from 22 to 18, increased the total production of biomethane by 11%, but also increased the levelised cost of energy. Approximately 1.8% of final thermal energy use could be met by 22 plants with a maximum size of 50 GWh/a, or 2% of final thermal energy use from 18 plants with a maximum size of 200 GWh/a. The biomethane from these plants is equivalent to 7.2%, and 8% of total industrial natural gas consumption in 2013/2014. (C) 2016 Elsevier Ltd. All rights reserved.