A simplified simulation model of heat storing fireplaces during combustion of residual thin char bed was developed. When the bed model is coupled with CFD calculations for the furnace above the bed, the emissions can be predicted. Especially the time instant of maximum CO emissions is considered. The following results (output quantities) can be calculated with the coke-bed model: bed temperature, composition of gases leaving from the bed (CO, CO2, O2 and NO), and release of carbon from the bed. The following input data are required: primary air rate, particle size, grate-area, bed thickness, bed porosity, and effective furnace radiation.