An embodiment of a system for ablating tissue comprises an electrode configured for use to deliver RF power to ablate the tissue, and a heat flow sensor configured to provide a measurement of heat flow from the electrode to blood or irrigation fluid. According to some embodiments, the system further comprises an RF source configured to generate RF power connected to the electrode (PE) to ablate tissue, and a controller configured to control a level of RF power and a duration for an ablation procedure. The controller is programmed to implement a process to estimate RF power dissipated in tissue (PT), including calculating power loss due to convective heat flow (PCONV) from the tissue through the electrode to the blood or the irrigation fluid to cool the electrode, and calculating the RF power dissipated in tissue (PT) by subtracting PCONV from PE.
