To meet EU climate goals, reducing fossil fuel use is crucial, and transitioning domestic energy consumption to sustainable sources like heat pumps offers a potential solution. However, uptake in Flanders remains low. This study explores predictors of heat pump adoption intention among Flemish homeowners using a mixed-methods approach. A quantitative survey based on an extended Theory of Planned Behaviour model (Study 1, n = 692, M_age = 55.03, SD_age = 15.54, male/female = 335/357) is complemented by semi-structured interviews with homeowners who do not own a heat pump (Study 2, n = 16, M_age = 41, SD_age = 35, male/female = 8/8). Study 1 indicates that perceived behavioural control and subjective norms positively influence heat pump adoption intention, with perceived behavioural control enhanced by product knowledge and technological innovativeness. Surprisingly, a positive attitude towards heat pumps is associated with a lower adoption intention. Study 2 reveals cost concerns, uncertainties about energy cost savings and property value increases as barriers to adoption intention, alongside a temporal disconnect between attitude and intention due to practical constraints. Our findings offer suggestions for communication strategies of policy makers such as addressing financial and practical barriers, mitigating practical constraints and enhancing public knowledge. Lastly, our survey results suggest the presence of yet unidentified moderating variables affecting the attitude-intention relationship, which could be determined in future research.