Leakages are inherently associated with the hear transfer process in a rotary heat exchanger owing to clearances brought about by construction difficulties and rotor-housing thermal distortions. The method proposed permits one to evaluate leakage distributions within steam boiler rotary regenerators. In principle, the method is based on a gas flow diagram of the regenerator, where gas streams are arranged into a network in which the corresponding mass flow rates are governed by pressure drops in the seals and matrix rotation. Moreover, energy and mass balances are taken into account where appropriate. On this basis, a nonlinear equation system modeling gas flows within the rotary regenerator is derived. Supplementing this system with data determined experimentally, one obtains a closed form of the gas flow problem, the solution of which gives particular gas mass flow rates within the regenerator and the leakage distribution resulting from it. On the basis of experiments carried out on real devices, the approach presented is exemplified with two particular cases accompanied by evaluation of uncertainties in the final results. A comparison of the results presented with those available by another method concludes the article.