National survey of indoor thoron concentration in FYR of Macedonia (continental Europe - Balkan region)

► The indoor 220Rn concentrations show seasonal and regional variability. ► The amplitude of seasonal variability is smaller for 220Rn, than for 222Rn. ► Indoor 220Rn map of FYR of Macedonia. ► The influence of house characteristics were analysed and discussed. ► Recommendations for future investigation were made.