Preventing air pollution

Boiler or furnace chimney and emission limits


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.

Authorisations for boilers and furnaces

You must make sure that you comply with any emission limits required by permits or authorisations.

Chimney height 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.

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.

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

Boiler emission 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.

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 checking and controlling air pollution.

Good practice to limit emissions

Inspect your emissions regularly so you can detect problems early. Plan and carry out maintenance to ensure that your furnace and boiler meets air emission standards and operates efficiently.

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