Class N – Flue for biomass heating system on commercial


flue for biomassWhilst you do not need planning permission for a biomass heating system, you will need an external flue for the biomass boiler. 

For commercial properties this is covered under Class N of Part 14. 

The capacity of the biomass system cannot exceed 45 kilowatts thermal on a commercial property for this flue, if it does you will require planning permission. 

As long as the flue does not extend more than 1 metre above the highest point of the roof or in the case of a conservation area or world heritage site isn’t on a wall or roof slope facing a highway you are fine. You will not require planning permission. The height can be exceeded if replacing a taller flue.

Apart from these two minor restrictions on a flue for a biomass heating system you can crack on. 

If the building is listed you will require listed building consent and planning permission .

Biomass is a renewable energy source, generated from burning wood, plants and other organic matter, such as manure or household waste. It releases carbon dioxide when burned, but considerably less than fossil fuels.

Biomass heating systems burn wood pellets, chips or logs to provide warmth in a single room or to power central heating and hot water boilers.

For the residential version of this, please see Class E of Part 14.





Class N – installation etc of flue for biomass heating system on non-domestic premises

Permitted development

N. The installation, alteration or replacement of a flue, forming part of a microgeneration biomass heating system, on a building other than—

(a) a dwellinghouse or a block of flats; or
(b) a building situated within the curtilage of a dwellinghouse or a block of flats.

Development not permitted

N.1 Development is not permitted by Class N if—

(a) the capacity of the system that the flue would serve exceeds 45 kilowatts thermal;

(b) the height of the flue would exceed either—
(i) the highest part of the roof by 1 metre or more, or
(ii) the height of an existing flue which is being replaced,
whichever is the highest;

(c) the installation of the flue would result in the installation on the same building of more than 1 flue forming part of either a biomass heating system or a combined heat and power system;

(d) the flue would be installed on a listed building, within the curtilage of a listed building or on a site designated as a scheduled monument; or

(e) in the case of a building on article 2(3) land, the flue would be installed on a wall or roof slope which fronts a highway.



Page Updated:  7th March 2023