A method for preheating a rotatable fluidizable bed (106) comprises rotating the bed chamber (112) slowly to cause the particles (114) to slowly tumble and mix. During tumbling, one or more burners (150, 160) extending into the chamber (112), heat the particles (114) until the desired operating or ignition temperature is reached. Temperature sensors (170) in thermal communication with the bed particles (114) sense the temperature and provide either an indication thereof or an initiating signal which, in the case of a rotating fluidized bed combustor (10), terminates preheating, accelerates the bed chamber (112) rotation to normal combustor (10) operating speed and/or introduces fluidizing air and/or fuel flow through the bed chamber (112).