Exposure to high temperatures leads to an increase in disease and mortality. Studies on the relation between high temperatures and mortality are always related to the temperature measured outside. But elderly people mostly stay indoors? To what extend is the inside temperature determined by weather conditions, urban and architectural qualities, and behaviour? In cooperation with the University of Utrecht and GGD Gelderland-midden, GGD Groningen investigated the underlying relationship between these factors. This is probably the first study on the importance of considering a wide range of factors that may influence heat exposure and its effects on people’s health. Will the prevention of heat islands be sufficient, or do we also have to look at our building tradition and possible other factors?