Stepping stones or carbon lock-in? Homeowner preferences for biofuels and heat pumps in residential heating decarbonisation

Decarbonising residential heating in Europe and North America depends on millions of individual household decisions. While policy has largely focused on replacing fossil-fuel boilers with heat pumps, slow progress has prompted growing interested in alternatives. Lower-carbon “drop-in” fuels such as hydrotreated vegetable oil (HVO) and biomethane are one type of alternative that can be used within existing heating systems relatively straightforwardly. Whether promoting such biofuels accelerates decarbonisation by acting as a stepping stone towards heat-pump adoption or instead delays it by reinforcing incumbent technologies has received much debate, but little direct empirical attention. We generate evidence for this debate using a survey experiment with a nationally representative sample of Irish homeowners with gas or oil boilers (N > 1,000), in which all respondents evaluated both a biofuel option and a heat pump, with the order of exposure randomised. Awareness of biofuels was low, particularly for biomethane. Initial willingness to switch was high and driven primarily by the ease of switching, but fell sharply once respondents learned about higher fuel costs and sustainability concerns. Heat-pump evaluations also declined as information was revealed, especially following disclosure of building-fabric retrofit requirements. Despite these declines, final willingness-to-switch remained substantially higher for biofuels than for heat pumps. Critically, exposure to biofuels did not reduce subsequent willingness to adopt a heat pump, with a point-estimate that was in-fact positive, providing no evidence for household-level carbon lock-in. The findings suggest that promoting lower-carbon fuel alternatives need not undermine support for electrification, though the attractiveness of both pathways remains strongly conditioned by their perceived financial and practical costs.