Over 50 % of naturally occurring radiation exposure is due to ²²²Rn (progenies), but traceability of measurements to the International System of Units (SI) is lacking. To address this, two new ²²²Rn sources were developed to be used as calibration standards for reference instruments. These sources were investigated by comparing their estimated calibration factors for one instrument. Despite the small differences derived, all uncertainties are well within the intended target uncertainty of 10 %.