Consideration is given to some of the scaling problems involved in the application of turbulent heating to much larger toroidal systems than those employed up to now. Single-pulse heating is studied in a model in which the time variation of the skin depth is allowed for and energy transport from the skin to the interior of the plasma maintains the poloidal beta factor, βp, at a constant value. With the total heating current limited to a value Im (for a safety factor q > 1), the ion acoustic instability can be generated only as long as the skin depth δ satisfies the condition δ < Im/(necs2πa) where n is the plasma density, cs the ion sound speed and a is the minor radius. Consequently, depending on the efficiency of the energy transport, it is not certain that single-pulse heating can raise the plasma temperature to that required for ignition of a fusion reactor, and some form of multiple-pulse-heating may be required.