Emergency department data from seven US states reveals that patients with documented social determinants of health face dramatically higher heat-related health risks. Among 60.5 million ED visits, those with Z-codes indicating poverty, inadequate housing, or social isolation showed consistently elevated temperature-morbidity associations across multiple conditions. The most striking finding involved acute kidney injury, where socially disadvantaged patients had 21% higher odds of heat-related episodes compared to matched controls. This represents the first large-scale quantification of how social vulnerabilities amplify physiological heat stress. The findings illuminate critical health equity gaps in climate adaptation. People experiencing homelessness, poverty, or social isolation likely lack access to air conditioning, adequate hydration, or social support networks during heat waves. These results suggest that climate health interventions must address underlying social determinants rather than treating temperature exposure as an equal-opportunity health threat. However, this preprint analysis awaits peer review, and the observational design cannot establish causation. The 0.8% prevalence of social determinant codes likely underestimates true vulnerability, as healthcare providers inconsistently document social conditions. This research provides compelling evidence that climate health policy requires targeted interventions for socially disadvantaged populations, potentially representing a paradigm shift toward equity-centered heat preparedness strategies.