© 2016 The Authors. The likely installation of, and potential energy savings from, low carbon technologies in domestic buildings is not only dependent on those who fit them, but also the broader supply chains of which they are part. Despite this, the role of supply chain actors has been largely overlooked in strategies seeking to encourage the installation of more sustainable domestic heating technologies. With reference to central heating, this paper responds through an ethnographic analysis of how plumbers' merchants and sales representatives can influence the work of heating installers in the United Kingdom. It applies two dimensions of the concept of 'social capital': relational and structural. Relational social capital focuses on the trust, loyalty and reciprocity at play in relations, whilst structural social capital considers how the strength of tie can influence those to whom people turn for advice and support. Together, these ideas demonstrate how relationships amongst these groups can serve to influence product choice and facilitate information exchange. The paper concludes by discussing how these supply chains might be engaged with as a means of encouraging the installation of low carbon domestic technologies.