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Using passive sampling techniques, including a passive sampling, multiple tracer gas technique (the PFT-technique), the Danish Building Research Institute has performed field measurements in about 130 dwellings. The dwellings comprised detached, naturally ventilated single family houses and single family houses and flats ventilated with exhaust ventilation systems. The object of the measurements was, in each of the types of dwellings, to determine the level of the outdoor air exchange rate, the level of the relative humidity and the level of the concentration of organic vapors in the indoor air. Also a simple questionnaire was elaborated in order to obtain information on the occupants and their airing habits.
The average outdoor air exchange rate in dwellings equipped with mechanical exhaust systems was found to be approximately 0.5 [h-1]. Naturally ventilated dwellings had an average outdoor air exchange rate of about 0.35 [h-1]. The relative humidity was in average just below 45 pct. both in mechanically and naturally ventilated dwellings. Neither the relative humidity nor the concentration of organic vapors showed any correlation with the outdoor air exchange rate.