A key mechanism of contemporary climate policy is to stimulate economic competition in technology markets to ensure more efficient energy use. But, what are the consequences of such incentive-based mechanisms for achieving decarbonisation in practice? I focus on heat pumps, both large and small, that are installed in households to replace oil and gas boilers and within district heating systems to use industries’ excess heat. In this study, from Big Tech datacentres. This is to examine whether climate policy is successfully translated into practice. Based on ethnography with public utility engineers of district heating in Odense, Denmark, complemented with document analysis of policy text, I chart three epistemic arrangements in decarbonisation work with attention to energy conservation, economic competition, and infrastructural connections. The epistemic practice of energy conservation is marginalised as competition mechanisms dominate climate policy instruments. The engineers’ efforts to comply and resist during infrastructural connection-making, in turn, showcase the limited mobilization of policy mechanisms that instruct decarbonisation as a contrast to policy mechanisms that try to incentivize decarbonisation. Learnings on how to best mobilise epistemic practices necessarily will have to go both ways between knowledge traditions on thermodynamics and market dynamics. Ultimately, hyperscale energy consumers such as Big Tech are configured as key agents to successful decarbonisation rather than energy conserving agents that, as utilities, are targets of climate policy. These findings challenge assumptions on whether policy mechanisms are constructed to effectively limit climate change and it suggests knowledge inclusions to increase decarbonisation via critical energy conservation efforts.