Typically planning permission is not needed when installing a biomass boiler in a domestic property as long as all the works are internal. A flue will always be required, but as long as it is on the rear or side of the building and does not exceed 1m above the highest part of the building, then it is considered permitted development. If however a building is listed or in a designated area, it is advisable to check with your Local Authority as consent may be required. More information on this can be found on the governments planning portal website.
As a simple rule, most non-domestic biomass boiler installations will require planning permission when the boiler is over 45kW in size. Where the boiler is 45kW or below in size, and the flue is not higher than 1m above the tallest part of the building, then the installation can come under permitted development. Some biomass systems may require a new building to be constructed for the plant room and fuel store, so this may also require planning permission. More information on this can be found on the governments planning portal website.
Even if you believe that the installation of a biomass boiler comes under permitted development, we would always recommend that you check with the Local Authority and obtain written confirmation planning permission is not required.
It is also a requirement of the RHI that planning permission is obtained where applicable, and this needs to be evidenced as part of the RHI application.