A Pr < 1 thermal flow around a fin at different positions on the thermal wall is investigated using scaling analysis and numerical simulation. Dynamic and heat transfer of the thermal flow around the fin with unsteady and steady flow rates are analyzed and possible flow regimes are identified. The scaling relations of the thermal flow around the fin are obtained, which are dependent on the fin position, the Prandtl number and the Rayleigh number. The velocity and thickness scales of the intrusion and the plume around the fin are also validated by numerical simulation. The numerical results are consistent with the scaling predictions. (C) 2017 Elsevier Ltd. All rights reserved.