Dynamic analysis of a boiler is accomplished by certain approximations which reduce the nonlinear partial differential equations to linear ordinary time-differential forms, and make it possible to obtain the time-dependent functions of large numbers of boiler variables. Linear equations thus obtained are solved by means of an electronic differential analyzer and open-loop response of drum pressure and water level for various input variables (feed-water rate, fuel-flow rate, and steam-flow rate) are shown as examples. A linearly controlled response of the same boiler is also given as an example of the flexibility of the method and the analog solution. It is shown that the potentiality of the method is not limited to this initial study, but can be extended for greater accuracy with the availability of machine computation. Analog simulation of the boiler also makes it possible to investigate the effects of the boiler physical dimensions, heat, or mass-transport constants and to verify some of the basic assumptions on the dynamic behavior of the over-all system.