Heat waves associated with global warming are a significant hazard to human health, and they particularly endanger low-income households. In this study, we systematically analyze how the different components of heat vulnerability are related to household income, and present empirical evidence on the determinants of heat adaptation, focusing on the role of income. We contribute the first empirical analysis of heat vulnerability using household-level data at the national level, based on a longitudinal survey, including data points for 10,226 households in Germany in the period 2012-2020. Our results indicate that low income households are significantly more heat sensitive and have lower adaptive capacity than high income households, measured inter alia by health status, household composition, and economic and psychological resources to implement adaptation measures. However, heat hazard and exposure levels are comparable between income groups, hence there is no sorting of richer households into less hazardous or exposed locations on a national scale. We also contribute robust empirical evidence on the factors influencing household decisions to implement technical adaptation measures (e.g. installation of air conditioning), ultimately showing that the adaptation behavior of the most vulnerable households (e.g. people with poor health conditions or the elderly) is not limited by financial constraints.