High in-bed heat transfer and low corrosive environment imply that the loop seal of a circulating fuidized bed (CFB) boiler is an advantageous location for superheaters. In order to increase the knowledge on the flow pattern and the heat transfer distribution to the tubes within a loop seal, measurements were performed in the loop seal of a 30 MW CFB boiler as well as in a 1/3 scaled-down seal operated according to simplified scaling laws. The scale model measurements show that the solids recirculation flux can be maintained with a substantial decrease of the fuidization flow in the seal compared to that currently used at full load conditions. It was also possible to significantly decrease the fraction of the bottom of the seal that was fuidized without affecting the solids flux through the seal. A gradient in the solids flow were detected in the vertical direction.