Display omitted Acceptable indoor air quality (IAQ) is one of the most relevant aspects of a healthy home environment. Despite advances in mechanical and hybrid ventilation systems, natural ventilation still constitutes a crucial intervention to improve IAQ in existing homes; especially in older and/or vulnerable ones. The challenge, however, is optimizing natural ventilation strategies so IAQ is reached while thermal discomfort (and potentially associated energy consumption) is minimized. The complexity of identifying factors that may determine the possibilities of natural ventilation in existing homes has traditionally hindered the efforts from the scientific community to communicate straightforward answers for end-users. This work develops a methodology that, based on real case studies and through a series of simulations, provides simple, context-specific criteria and recommendations in order to reach acceptable IAQ through natural ventilation strategies in existing homes. The use of a minimum ventilation time (MVT) indicator, alongside considerations for different seasons and housing types, are translated into step-by-step guidelines aimed at helping the end-user to (i) gain knowledge regarding the opportunities and limitations for natural ventilation in the dwelling, and (ii) identify which specific actions should be carried out under different conditions to maintain minimum IAQ. The conceptual framework and methodology presented, while illustrated for the case of Barcelona, can be replicated for different cities or regions with differing housing characteristics and climatological conditions, and can easily accommodate other locally relevant factors.