Changes in indoor climate after tightening of apartments

The effect of reduced air infiltration rate caused by energy-saving measures has been studied by comparing the indoor climate in 25 sealed apartments with the conditions in 25 unsealed apartments in four seasonal periods. The indoor temperature in bedrooms during February and March was 19.3 °C in sealed apartments and 17.8 °C in unsealed apartments, and the occupants in the sealed apartments correspondingly complained less frequently of draught problems during the winter. When the frequency of window opening was at its minimum (February–March), there was a higher indoor humidity in sealed compared with unsealed apartments, and this probably accounts for an increased occurrence of house-dust mites in dust from the sealed apartments during the winter. Also in February–March there was a slight increase in the concentration of suspended particulate matter in sealed apartments. Considering health effects of a reduced air infiltration rate, it can be predicted that the increased indoor air humidity will indirectly increase the frequency and severity of house-dust mite allergy in the population.