A computer simulation model for furnace and boilers was developed, which calculates the thermal state of a boiler using the method of indirect determination of the boiler efficiency.

All the variables used in the model are measurable on a test bench under standardized conditions. As the profile of the flue gas temperature and the air temperature at the outlet of the boiler can easily be determined, it is possible to calculate the losses through the chimney during the burner-on and the burner-off times respectively.

However, the temperatures and the heat transfer within the boiler are not generally measured. Therefore, the boiler is considered as an ideal storage unit with an evenly distributed temperature. The surface losses of the boiler are computed using two mean U.A.-values.

Several parametric studies are made using this model.