Detached house owners can improve energy efficiency in heating by adding a supplementary heating system alongside the primary mode. Whereas research on primary heating mode adoption is wide, studies focusing solely on the determinants of supplementary heating system adoption is limited. This study examines the determinants of supplementary heating system adoption and consideration in Finland with a survey data collected from a sample of newly built detached house owners. We employ discrete choice modeling to investigate the homeowners’ supplementary heating system choices and interpret the results vis-à-vis the diffusion of innovations literature. The supplementary heating systems under study are solar panel, solar thermal heater, air-source heat pump and water-circulating fireplace. Overall, the findings indicate that homeowners are generally receptive to supplementary heating in Finland. The analyses show that several factors such as age, education, primary heating mode, heating system attributes, location, environmental attitudes and information channels impact the supplementary heating system adoption decision.