This thesis starts by describing research on the design of low frequency induction heaters using a series equivalent circuit model. Limitations associated with this design method are explained. An alternative called the transformer equivalent circuit (TEC) model is then presented. This models the induction heater as a single turn secondary transformer. Its advantage is that the currents and voltages associated with components of the induction heater are what you would expect to measure on components of an actual induction heater. Finite element analysis (FEA) is also used to predict the performance of induction heaters. The performances of these models are compared, with experimental veri cation on a small induction heater unit. The research is then extended to transduction heaters, a combination of transformer and in- duction heaters, which include a secondary winding to boost performance. The transformer equivalent circuit method is used to predict the performance of transduction heaters as they cannot be modelled using the series equivalent circuit model. The performances of the trans- former equivalent circuit and nite element analysis models are compared with results from a set of experimental transduction heaters. Modi cations are then made to the components of the TEC model to improve its performance predictions. The accuracy of TEC modelling is con rmed with a second design and veri ed with experimental results. This forms the basis for the nal design and implementation of an industrial unit. The improved TEC model is then used to predict the performance of a 40kW transduction uid heater that was designed, built and tested. Comparisons are made between the TEC and FEA models calculated results and test results. The TEC calculated results yielded much closer values to those measured.