As a result of the development of wind farms,the gas- steam blocks,which shall quickly ensure energy supply in case the wind velocity is too low,are introduced to the energy system.To shorten the start-up time of the gas-steam and conventional blocks,the structure of the basic components of the blocks are changed,e.g.by reducing the diameter of the boiler,the thickness of its wall is also reduced.The attempts were also made to revise the currently binding TRD 301 regulations,replacing them by the EN 12952-3 European Standard,to reduce the allowable heating and cooling rates of thick walled boiler components.The basic assumption,on which the boiler regulations allowing to calculate the allowable temperature change rates of pressure components were based,was the quasi- steady state of the temperature field in the simple shaped component,such as a slab,cylindrical or spherical wall. As a result of the development of wind farms, the gas-steam blocks, which shall be quick to ensure energy supply in case the wind velocity is too low, are introduced to the energy system.To shorten the start-up time of the gas-steam and conventional blocks, the structure of the basic components of the blocks are changed, egby reducing the diameter of the boiler, the thickness of its wall is also made to revise the currently components binding the TRD 301 regulations, replacing them by the EN 12952-3 European Standard, to reduce the allowable heating and cooling rates of thick walled boiler components. the basic assumption, on which the boiler regulations allow to calculate the allowable temperature change rates of pressure components were based, was the quasi- steady state of the temperature field in the simple shaped component, such as a slab, cylindrical or spherical wall.