Skip to main content  


Most of the air pollution in the City is cause by road traffic. However, it is estimated (via the London Atmospheric Emissions Inventory ) that around 33% of NOx and 9% of PM10 emissions come from boilers, CHP and generators. Wood burning outside the City boundary also impacts on London PM10 levels.

Several measures are in place to minimise boiler, CHP and generator emissions, where possible.​ Newly installed boilers and CHP must meet low NOx emission​ limits; see the GLA's Sustainable Design and Construction SPG​ or the City Corporation's Air Quality SPD for more guidance.

The City of London has also produced a short guidance note aimed at minimising emissions from standby generators (270KB).

Clean Air Act 1993

Some chimneys serving furnaces or boilers require approval from the City of London Corporation before they are used. This is to ensure that the proposed chimney is high enough to allow adequate dispersion of the flue gases.

Approval is required for chimneys serving commercial or industrial furnaces or boilers used to burn the following fuels:

  1. Pulverised fuel
  2. Any other solid matter at a rate of 45.4 kilograms/hour or more.
  3. Any liquid or gaseous matter at a rate of 366.4 kilowatts/hour or more

Chimney height approval is required in addition to any other necessary permissions e.g.​ planning permission or building regulation approval.

Chimney height applications

Download a chimney height application form (25KB) or contact the City of London for an application form. The City of London will to determine the application within 28 days of receipt. There is no charge.

Applicants should use the 3rd Edition of the Clean Air Act Memorandum on Chimney Heights for guidance in order to establish the height of any proposed chimney. This document is published by Her Majesty's Stationery Office (HMSO).

Further information

City of London
Department of Markets and Consumer Protection
PO Box 270, Guildhall
London EC2P 2EJ

020 7606 3030