A city’s materiality creates health and illness. We both write about air – its movement and its temperature – as it aﬀects human bodies. We oﬀer two topics as case studies, heat and ventilation, and how they exacerbate the eﬀects of each other, to illustrate the long history of seemingly new challenges posed by the novel coronavirus. The environmental inequalities of heat exposure and access to fresh air underscore that cities can only be considered ‘low impact’ on the environment from a top-down, large-scale approach. In writing about air and heat, we direct attention to the feel and the bodily impacts of unseen but persistent problems in housing. Centuries of building inequalities into the urban environment are coming to bear on our present debates about indoor space, ventilation, and viral spread as cities encounter the COVID-19 crisis.