Environmental guidance for your business in Northern Ireland & Scotland

Boilers and furnaces - chimney and emissions requirements

Boilers and furnaces: chimney and emissions requirements


A boiler or furnace burning fuel normally releases smoke through a chimney. Smoke darker than a specified shade of grey is officially classified as 'dark smoke'. You must not cause or allow emissions of dark smoke from your chimney. See the page in this guideline dealing with dark smoke restrictions.

Authorisations or permits for boilers and furnaces: You must make sure that you comply with any emission limits required by permits or authorisations. See the page in this guideline that covers boilers and furnaces  - environmental authorisations or permits.


What you must do

Chimney height requirements and other chimney requirements

Your chimney must be high enough to prevent smoke, grit, dust, gases and fume emissions from damaging health or causing a nuisance. Your local council can refuse approval for a chimney that is not a sufficient height.

You must obtain approval from your local council for a chimney by satisfying them that your chimney will be tall enough to prevent its emissions becoming a nuisance.

In Scotland you must apply for chimney height approval from your local council, if:

  • you do not have a pollution prevention and control permit
  • your boiler's fuel consumption exceeds 45.4 kilograms of solid fuel per hour
  • your boiler's fuel consumption exceeds 366.4 kilowatts of liquid or gas fuel per hour.

In Northern Ireland and Scotland, your application must contain details of:

  • the purpose of the chimney
  • the position and type of local buildings
  • local ground levels
  • any other issues that must be taken into account.

Your local council may apply certain conditions to their approval such as the rate and quality of emissions from your chimney.

A chimney may be exempt if it is used as 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
  • an auxiliary plant to bring the main plant up to operating temperatures
  • a mobile source of heat or power for agricultural purposes.

If your use of the chimney changes you must re-apply for approval for the new emissions.

In most cases a chimney or stack should have no restriction on the top, as this could reduce the dispersion of emissions. This may be a requirement, part of the local council conditions of operation for the chimney or stack.

You are committing an offence if you use the chimney without approval from your local council.


​Emissions requirements


You must fit all boilers with grit and dust arrestment equipment. You can apply to your local council for an exemption, but this will only be granted if the boiler will not create emissions that could damage health or cause a nuisance. For further information you should contact your local council.
Find your local council

Smoke, grit and dust emission limits

Your local council can apply limits on emissions of smoke, grit and dust you produce. If you exceed these limits you may be committing an offence and could be prosecuted. Your local council is likely to set limits for sites with a history of complaints, or sites that use fuel or procedures they were not designed to use.

You should use the best practical means to minimise emissions, for example:

  • fit grit and dust arrestment filters
  • inspect boilers, furnaces and filter equipment regularly for correct operation
  • install filter performance monitors.

See the page in this guideline that covers checking and controlling air pollution.


Good practice

Check your emissions regularly so you can detect problems early. Make a record of these measurements.

Plan and carry out regular maintenance, to ensure that your furnace and boiler meet air emission standards and operate efficiently.

Use cleaner fuels, such as gas, to limit the environmental impact of your furnace and boiler.


In this guideline

Causes and effects of air pollution

Business benefits of improving air quality

What you must do to prevent air pollution

Prevent dark smoke

Boilers and furnaces: environmental authorisations

Boilers and furnaces: Chimney heights

Burning waste controls

Smoke control areas

Protecting neighbours from air pollution

Measuring and monitoring to reduce air pollution

Air pollution environmental legislation

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