Determining　ventilation　rates　is　helpful　to　study　indoor　air　quality　(IAQ).　This　paper　investigated　the　natural　ventilation　of　three　households　in　Beijing,　using　exhaled　CO2　as　the　tracer　gas　to　calculate　and　determine　the　ventilation　rates.　Also　it　considered　ventilation　conditions　in　different　seasons,　in　different　outdoor　air　quality,　and　in　different　outdoor　temperatures.　The　results　show　that　there　are　seasonal　differences　in　window　opening　behavior,　and　outdoor　temperature　has　a　more　significant　effect　on　window　opening　behavior　than　that　outdoor　air　quality.　The　data　obtained　in　this　study　and　its　analysis　is　thought　useful　as　a　reference　source　for　other　studies　of　energy-saving　ventilation　systems.　©　2020,　Springer　Nature　Singapore　Pte　Ltd.