Planning permission is not normally needed when installing a biomass system in a house if the work is all internal. The installation of a flue outside is normally permitted development, unless it affects the roof line, at which point planning permission should be sought.
Disclaimer - Wales
This is an introductory guide and is not a definitive source of legal information. This guidance relates to the planning regime for Wales. Policy in England may differ. If in doubt contact your Local Planning Authority.