Biomass boilers burn wood chip or wood pellets to produce water at the same temperature as oil or gas boilers, but the fuel comes from a sustainable supply rather than a fossil fuel.
Biomass boilers are basically just very efficient wood burners; their operation is easy to understand, the wood burns and the heat produced is used to heat water that is then used to heat a property or a hot water tank. However, the key thing with a biomass boiler is that is designed to burn the fuel as completely and efficiently as possible, very little of the heat produced is wasted and the amount of ash created is minimal when compared to a conventional open fire or wood burner.
The fuel that can burned in biomass boilers is very tightly controlled if RHI payments are to be expected from the system to ensure that the system will perform as efficiently as possible. The fuel will need to be of an approved type, from an approved supplier and the moisture and calorific values of the fuel will have to be within approved guidelines.
Biomass systems do require a flue to expel waste gases safely which can effect where they can be installed in the property.
Temperature of the hot water produced
Because the heat produced is via combustion, biomass boilers will typically produce hot water that is at the same temperature as a conventional gas or oil boiler would, around 65 degrees celsius. As such, biomass boilers can be easy to retrofit into existing properties because the heat emitters (radiators) will likely have already been designed to operate at these temperatures.
Biomass boilers can work with underfloor heating systems, but the temperature of the water that is passing through the underfloor heating pipes will need to be blended down to a lower temperature to ensure that the floor slab is not damaged, this is typically about 40 degrees celsius.
Biomass systems do require more maintenance that most other types of renewable heating systems.
The fuel that is burned by the biomass boiler will need to be replaced on a frequent basis, how frequent depends on the system install and the size of the hopper that will contain the source fuel. The fuel can be delivered in bags (which will need to be emptied into the hopper) or possibly delivery by a truck that can blow the fuel into a large storage bag / hopper. The later requires a lot less effort, but would typically require a larger more expensive hopper / storage container.
The ash that is produced will also need to be removed from the boiler on a reasonably frequent basis. The amount of ash produced and how frequently it needs to be emptied will again depend on the system installed and the fuel type that is burned, but it would never be more than daily, typically only weekly.