Heat waves can be lethal and routinely prompt public warnings about the dangers of heat. With climate change, extreme heat events will become more frequent and intense. However, little is known about public awareness of heat warnings or behaviors during hot weather. Awareness of heat warnings, prevention behaviors, and air conditioning (AC) prevalence and use in New York City were assessed using quantitative and qualitative methods. A random sample telephone survey was conducted in September 2011 among 719 adults and follow-up focus groups were held in winter 2012 among seniors and potential senior caregivers. During summer 2011, 79 % of adults heard or saw a heat warning. Of the 24 % who were seniors or in fair or poor health, 34 % did not own AC or never/rarely used it on hot days. Of this subgroup, 30 % were unaware of warnings, and 49 % stay home during hot weather. Reasons for not using AC during hot weather include disliking AC (29 %), not feeling hot (19 %), and a preference for fans (18 %). Seniors in the focus groups did not perceive themselves to be at risk, and often did not identify AC as an important health protection strategy. While heat warnings are received by most New Yorkers, AC cost, risk perception problems, and a preference for staying home leave many at risk during heat waves. Improving AC access and risk communications will help better protect the most vulnerable during heat waves.