An immersed boundary method (IBM) has been developed for the study of fluid-flexible body interactions with heat transfer. The fluid motion and temperature are defined on a fixed Eulerian grid, while the flexible body motion is defined on a moving Lagrangian grid. The governing equations for the fluid motion, the temperature, and the flexible body motion are solved independently on each grid system. To handle the momentum transfer between the flexible body and the surrounding fluid, the additional momentum forcing obtained by using the feedback forcing law is added to the fluid and body motion equations, enforcing the no-slip boundary condition of the fluid on the flexible body. The additional heat source between the heated body and the surrounding fluid can be calculated in a similar way to that used for obtaining the momentum force, which enforces the specified thermal boundary conditions on the body. The stability tests for the feedback forcing constants for the fluid-body interactions and the heat transfers are performed. Natural and forced convection problems with the isothermal and constant heat flux boundary conditions are simulated with a good agreement with those of previous studies. The simulations for the forced convective heat transfer around a flexible circular cylinder are performed. Two distinct stable states are observed depending on the Reynolds number and the flexible property of the cylinder, i.e., stretched-stable and self-sustained flapping states. The convective heat transfer is deteriorated for the stretched-stable state due to the elastic deformation, while enhanced up to 7% for the self sustained flapping state compared to the heated rigid cylinder. The transverse pitching motion is related to the mean heat transfer during one flapping period. The longitudinal tapping motion determines when the heat transfer is maximized or minimized in the flapping cycle. (C) 2017 Elsevier Ltd. All rights reserved.