This paper describes a new experimental method for measuring stator heat transfer in a rotor-stator disc system using an electrical heater array. The system is partially blocked at the periphery, with radial outflow of rotor-pumped air from an inlet at stator centre. The aim is to improve thermal performance prediction for air-cooled disc type electrical machines. Local Nusselt numbers were measured for 0.6 < r/R < 1 at three non-dimensional gap ratios G = g/R = (0.0106, 0.0212, 0.0297) and rotational Reynolds numbers 3.7e4 <= Re-theta <= 5.6e5. Transition at the stator is observed to occur at Re-theta > 3e5 for all gap ratios. Increased Nusselt numbers at the periphery are observed for all Reo and G because of the ingress of ambient air along the stator due to the rotor pumping effect. (C) 2009 Elsevier Ltd. All rights reserved.