A field study conducted in a modern Nordic single-family house with high airtightness and insulation levels, attempted to control summer indoor overheating using night-time cooling strategies. Exhaust air flow rates were manually scheduled by the researchers (based on weather forecasts), analogous to what an engaged occupant - or a predictive system - might do. Air temperatures at a nearby meteorological station peaked at 30 °C during 6 days in June that saw only 44 hours below 18 °C. Temperatures recorded indoors at the test house reached 32 °C, due also to very large solar gains, and never fell below 26 °C over 8 continuous days. It appears that under extended heat conditions that are exceptional now, but foreseen to become more frequent, some modern Nordic homes cannot be temperature controlled by ambient ventilation alone.