The carbonate looping process using the reversible calcination/carbonation reaction of limestone is a promising way to reduce CO2 emissions of fossil fired power plants. This paper describes the concept of an indirectly heated version of this process in which heat pipes accomplish the heat transfer from an air-blown fluidized bed combustor to a bubbling fluidized bed calciner. It defines the calciner's specific heat demand which is a pendant to the heating value of coal. The dimensioning depends on the processes inside heat pipes as well as heat transfer of immersed heating surfaces. Experimental investigations in an electrically heated batch reactor with a similar pipe grid provide heat transfer coefficients under calcination conditions.