The two types of fluidised bed furnaces commonly distinguished are the circulating fluidised bed furnace and the bubbling fluidised bed furnace. The bed material, usually sand, is finer for the circulating fluidised bed furnace than for the bubbling fluidised bed furnace, 0.3 and 2 mm respectively. Part of the bed is bled out to keep an acceptable chemistry in the bed: alkalis tend to dissolve in the sand and reduce

There are other types with special designs, e. g. cyclone furnaces, but they are not common.

the temperature at which the particles sinter together. The combustion temperature is low, approximately 850°C.

The largest part of the residue is fly ash. The proportion of bottom ash depends on how much material is bled from the bottom of the bed. Both streams of ash contain not only ash from the fuel but also bed material, oversized material in the bottom ash and fine particles from attrition in the fly ash.

The combustion temperature is too low to allow the Portland cement reactions in the fly ash (these require at least 1,400°C). However, they still have binding properties through other reactions which are not fully known. Because of the low combustion temperatures, the particles have irregular shapes. The compressive strength is good even in the green stage if they have been well packed. Among other properties, this makes them very good materials for road building. Mixed in equal proportions with digested sewage sludge, they also provide dense sealing layers to landfills.

The bottom ash contains mostly bed material. It is often too fine and has too narrow a size distribution to be useful in construction, other than as low-quality fill material. However, under certain circumstances, e. g. absence of binding properties, it could be used as backfill material in trenches for piping.