Chimney height approval

Why is chimney height approval required for certain chimneys?

The Clean Air Act 1993 introduced a range of regulations to control smoke emissions and the height of new chimneys. We approve chimney heights and associated arrestment plant of large boilers and furnaces to ensure that emissions are at a safe height and dispersed sufficiently into the atmosphere and not be detrimental to health, or cause a nuisance.

The application for chimney height approval enables us to take into account a number of relevant factors in determining the height of a chimney. These include the need to avoid down draught or down wash created by the chimney itself, or by buildings or topological features, to avoid the likelihood of the ground level concentration of combustion products becoming prejudicial to health, or a nuisance.

When is chimney height approval required?

We must approve the height of any chimney associated with a furnace (except a domestic furnace) or boiler if you burn:

  • Pulverised fuel;
  • At a rate of 45.4 kilograms or more an hour, any other solid matter; or
  • At a rate equivalent to 366.4 kilowatts or more, any liquid or gaseous matter.

If you are intending to carry out any of the following activities and any one of the above criteria apply, you need to apply to us for chimney height approval in:

  • Constructing a new chimney;
  • Increasing the combustion space of an existing furnace;
  • Adding a new furnace to an existing installation;
  • Changing the fuel burnt in an existing furnace; or
  • Replacing a furnace with one having a larger combustion space.

How much does it cost?

Application for approval is free of charge.

Application for chimney height approval

Complete a Chimney Height Approval Application Form (PDF 136Kb / 7 pages) if you wish to build a chimney. You must apply for consent first. If you would like a paper copy, please contact us. Once you have completed the application form, post or email the form back to us at the address given below. An application for chimney height approval must contain adequate information to enable us to carry out the necessary calculations.


Contact the British Library to request a copy of the Secretary of State guidance note: 'HMIP Technical Guidance Note D1: Guidelines on Discharge Stack Heights for Polluting Emissions', published by HMSO, ISBN 0-11-752794-7, as this guidance note is now out of print.

The third edition of the 1956 Clean Air Act Memorandum on chimney heights (issued with Joint Circular DoE 25/81 Welsh Office 12/81) also provides technical guidance.

Application process

We will consider the application and give a written decision within 28 days of receipt, unless we agree in writing a longer period. If we fail to deal with the application within the agreed time, approval without qualification is given.

We cannot approve the proposed chimney height unless we are satisfied that it will be sufficient to prevent, so far as is practicable, the smoke, grit, dust, gases or fumes emitted from the chimney from becoming prejudicial to health, or a nuisance, having regard to:

  • The purpose of the chimney;
  • The position and descriptions of buildings near to it;
  • The levels of the neighbouring ground; and
  • Any other matters requiring consideration in the circumstances.

We can attach conditions to the approval, such as the rate and quality of emissions from your chimney.

Stranger Science and Environment, at the request of the Department of Environment, Food and Rural Affairs, provide supplementary technical assistance for estimating the minimum permissible chimney height for small boilers emitting sulphur dioxide. Call them on 020 792 6119.

Exempt chimneys

A chimney may be exempt if part of:

  • A temporary replacement, for example, if the boiler or furnace is being repaired;
  • A temporary source of heat or power for building works;
  • Auxiliary plant to bring the main plant up to operating temperatures;
  • A mobile source of heat or power for agricultural purposes.

Control of dust and grit from furnaces

The Clean Air Act 1993 requires you to provide, subject to certain exemptions, furnaces with a heating capacity greater than 16.12 kilowatts with plant for arresting grit and dust, as approved by us. If your appliance has a capacity greater than 16.12 kilowatts, we may ask you to provide further information to satisfy these criteria.

Last updated: Tuesday, 1 October, 2019.