A dynamic mathematical model has been developed which predicts the transient temperature response of circulating fluidized bed (CFB) combustors as well as the corresponding transient carbon and oxygen concentrations in the bed. The model includes mass balances of oxygen and carbon, energy balances, as well as sub-models for the gas-solid flow structure, combustion, and heat transfer from the bed to both the refractory walls and to a waterwall located in the fast bed section. Model validation was successfully completed against data obtained from tests performed on the 0.3 MWt CFB pilot plant located at the Technical University of Nova Scotia in Halifax, Nova Scotia.