Accessing patients' social needs is a critical challenge at emergency departments (EDs). However, most EDs do not have extra staff to administer screeners, and without personnel administration, response rates are low especially for low health literacy patients. To facilitate engagement with such low health literacy patients, we designed a chatbot - HarborBot for social needs screening. Through a study with 30 participants, where participants took a social needs screener both via a traditional survey platform and HarborBot, we found that the two platforms resulted in comparable data (equivalent in 87% of the responses). We also found that while the high health literate participants preferred the traditional survey platform because of efficiency (allowing participants to proceed at their own pace), the low health literate participants preferred HarborBot as it was more engaging, personal, and more understandable. We conclude with a discussion on the design implications for chatbots for social needs screening.