The objective of this study is to investigate how measured ventilation rates in dwellings vary over the heating season in a Nordic climate. The aim is to draw conclusions about the possibility to transform a measurement result obtained during a relatively short period of time into one which would have been expected as an average over a whole season. If such normalisation of measurement data is not possible, dwellings may be misclassified as under- or over-ventilated, a matter which may dilute a possible relationship between health and air quality in epidemiological studies.

Passive tracer gas measurements of ventilation were performed in a detached single-family house and in a flat (apartment) in Stockholm during four consecutive winter seasons. Measured averages of air change rate data are reported for 47 two-week periods for those two naturally ventilated dwellings. Another measurement using two different tracer gases was performed in an airtight, extract ventilated detached house over one year. The variation of ventilation is discussed in terms of variation in the ventilation driving forces induced by inside-outside temperature differences. The naturally ventilated house shows a slightly better correlation between air change rate and indoor-outside temperature difference than the town flat. It is concluded that the correlations are not good enough for predictive use for either dwelling. Therefore it does not seem possible to “normalise” ventilation measurement data. A slightly better possibility to predict the weather influence exists for the airtight, extract ventilated house. A possible reason for the lack of good correlation between air change rate and natural driving forces is a highly variable influence from occupant behaviour.