Medium combustion plant: when you need a permit
Source: gov.uk (2025-07-09)

Find out if and by when you need to apply for a medium combustion plant directive (MCPD) environmental permit to meet air quality requirements.

A medium combustion plant (MCP) includes all the following:
- a combustion unit, such as an engine, boiler or turbine
- any abatement
- the attached stack or flue
- air cooling where it’s part of the combustion unit
A MCP does not include:
- fuel handling or storage
- waste handling equipment
- external water or air cooling
Use this guidance to work out if your MCP:
- is excluded from MCPD controls
- generates electricity, whether both the MCPD and specified generator regulations apply
- capacity is covered by the regulations
- is classed as new or existing
Excluded MCP

MCPD controls do not apply to all MCPs. Check if they apply to your type of MCP.

MCPs that are also under the Industrial Emissions Directive (IED)

MCPD controls do not apply to combustion plant which is:
- chapter 3 – large combustion plant
- chapter 4 – incinerators or co-incinerators
MCPD controls may apply to other combustion plant on these IED chapter 2 installations. Read how to meet MCPD requirements for IED chapter 2 installations (https://www.gov.uk/guidance/medium-combustion-plant-and-specified-generators-environmental-permits#ied-chapter-2-permits-affected-by-the-regulations).

MCPs that are also an environmental permitting Part B activity

Read the guidance on requirements for MCPs that are also a Part B activity (https://www.gov.uk/guidance/part-b-activities-combustion-and-incineration-permits).

Mobile MCPs and mobile boilers

MCPD controls do apply to mobile MCP placed on the market (for distribution or use) before 1 January 2017 and with an engine above 560 kilowatt (kW) drive output.

MCP placed on the market before 1 January 2017 but not operated for the first time until after 20 December 2018, is classed as a new MCP rather than an existing MCP. (See the section on ‘When a MCP is classed as new or existing’.)

MCPD controls do not apply to mobile MCP placed on the market after 1 January 2017. They are covered by the revised Non Road Mobile Machinery Regulations (NRMM) (http://www.legislation.gov.uk/uksi/2018/764/made). These regulations extended the scope of the previous NRMM Directive (engines up to 560kW drive) to include engines with no upper size threshold.

MCPD controls do apply to a mobile boiler on a trailer for transporting it from site to site.

On-farm combustion

MCPD controls do not apply to an on-farm combustion MCP if both of these apply, it:
- has a rated thermal input of 5 megawatts thermal (MWth) or less
- only uses unprocessed poultry manure as fuel
Animal by-product regulations control these MCPs.

If you use other types of manure (mixed or unmixed), the MCP is classed as using ‘other solid fuel’ and MCPD controls apply.

Direct heating and drying

MCPD controls do not apply to MCP using the gaseous products of combustion for direct heating, drying or other treatment of materials.

Examples of this include:
- annealing of metals
- brick manufacture
- vehicle spray booths which use combustion to condition the air
- asphalt plants which heat and dry aggregates before adding them to asphalt
- concrete block and precast concrete product manufacture which use heat to speed up the curing process
- mortar plants which heat and dry sand before adding it to the mortar
- chemical reactors which use a direct flame
- direct gas fired ovens which have the burner located within the oven chamber so that the hot combustion gases come into direct contact with the product
MCPD controls do apply to autoclaves that use steam because the steam is not a gaseous product of combustion. For example, aircrete block manufacture which use hot steam to speed up the curing process.

Direct gas-fired heating

MCPD controls do not apply to a MCP that uses the gaseous products of combustion for direct gas-fired heating to improve indoor workplace conditions. This is where the flame itself provides the heat, rather than where the flame heats a fluid that is then used to transfer heat to the surrounding work space.

Flare stacks

MCPD controls do not apply to flares for disposal of waste gases.

Combustion plant designed or used to purify waste gases

MCPD controls do not apply to post combustion plant designed to purify waste gases from industrial processes which do not run as an independent combustion plant. For example, a thermal oxidiser designed to destroy odour.

If a conventional combustion plant is used to abate odour by using malodourous gases as part of the boiler feed air, ELVs may not apply during that period. You should check the application of MCPD controls with your regulator.

This type of abatement will need to meet best available techniques (https://www.gov.uk/guidance/best-available-techniques-environmental-permits), if the combustion plant is part of a Part A or Part B installation.

Vehicle, ship or aircraft

MCPD controls do not apply to any technical apparatus used to propel a vehicle, ship or aircraft, including auxiliary engines in ships.

Offshore platforms

MCPD controls do not apply to gas and diesel engines and gas turbines installed on offshore platforms. See Schedule 25A (http://www.legislation.gov.uk/ukdsi/2018/9780111163023/regulation/16) to check the location requirements.

Refineries

MCPD controls apply to a MCP in a gas or oil refinery installation firing exclusively commercial fuels.

MCPD controls do not apply to a MCP in a gas or oil refinery installation firing:
- refinery fuel gas (RFG) alone
- refinery fuel oil (RFO) alone
- RFG or RFO combined with commercial fuels
MCPD controls do apply to a MCP firing these fuels adjacent to but independent from the refinery.

MCPD controls do not apply to these refinery activities:
- fluid catalytic cracking units including carbon monoxide heat recovery boilers
- sulphur recovery units that convert hydrogen sulfide to sulphur
Crematoria and cowpers

MCPD controls do not apply to:
- crematoria
- cowpers
Pulp recovery boilers

MCPD controls do not apply.

Research, development and testing

MCPD controls do not apply for:
- test beds for engines and turbines
- commissioning trials for a new combustion plant
- antique plant in museums – because they operate for less than 500 hours per year
Firefighting training facilities

MCPD controls do not apply because the training facility uses the smoke not the heat generated.

Capacity

MCPD controls apply to all in-scope MCPs with a rated thermal input of each unit equal to or greater than 1MWth and less than 50MWth, regardless of the type of fuel used or the number of hours of operation.

Rated thermal input is the capacity of the MCP. It’s calculated using the net calorific value (CV) not the gross CV.

You can:
- ask the manufacturer for this value
- calculate it using Association of Manufacturers of Power generating Systems (AMPS) method (https://www.amps.org.uk/wp-content/uploads/2023/06/AMPS-Guidance-for-determination-of-thermal-input-power-of-generators-.pdf)
- use the combustion engineers association boiler calculations guide for MCPD (https://cea.org.uk/boiler-calculations-for-mcpd/)
You must aggregate 2 or more separate MCP on the same site when the MCPs are new.

When a MCP is classed as new or existing

The date you must have your MCPD permit in place depends on whether your MCP is new or existing. A MCP is:
- new – if it’s put into operation on or after 20 December 2018
- existing – if it’s put into operation before 20 December 2018
‘Put into operation’ means the date the fuel is first combusted in the MCP. This includes when the plant is commissioned on a site but not conformity testing at the place of manufacture.

You must have proof of the date the MCP was put into operation. If the equipment is second hand this may have been by another operator at a different location.

The record must be traceable to the combustion unit through a unique identifier such as a serial number or manufacturer’s name plate.

An existing MCP will become a new MCP if it’s:
- altered or repaired and this changes the ELV for the worse, that is pollution levels are increased
- substantially refurbished and the refurbishment costs are more than 50% of what a new comparable MCP would cost
An existing MCP may be a Tranche B specified generator. Check the definition of a Tranche B generator (https://www.gov.uk/guidance/specified-generator-when-you-need-a-permit#more-time-to-comply--who-qualifies).

New or existing MCPs have different emission limit values (ELVs) to meet.

When you must aggregate (new MCPs only)

You can only aggregate new MCPs. Aggregating separate discharge points, for example stacks, can improve dispersion.

Form a single MCP by adding together the rated thermal input of 2 or more separate new plant on your site that discharge the waste gas through a common windshield.

A common windshield is a shared structure or stack and it may contain one or more flues.

Do not count any new units measuring less than 1MWth.

If, after aggregation, the combined thermal input is greater than 50MWth, you should check the rules for large combustion plant (https://www.gov.uk/government/publications/environmental-permitting-guidance-the-large-combustion-plants-directive).

Operators must not avoid aggregation:
- by separating discharge points
- to minimise costs
When the Environment Agency or Natural Resources Wales assess the aggregation, they’ll consider if:
- the separate discharges are a common windshield by looking at technical and economic factors – for example, whether safety rules require separate discharge points
- there’s no reason why the discharges cannot be aggregated by looking at parameters like distance, flow and back pressure
Permitting and compliance dates

You must apply for your permit and have it in place by:
- 20 December 2018 or before it’s commissioned, whichever is the later, if it’s a new MCP – you can apply now
- 1 January 2024 if it’s an existing MCP and the capacity is greater than 5MWth and less than 50MWth – you can apply now
- 1 January 2029 if it’s an existing MCP and the capacity is equal to or greater than 1MWth and less than or equal to 5MWth – you cannot apply yet
You must comply with your MCPD permit by:
- 20 December 2018 or from date of issue if it’s a new MCP
- 1 January 2025 if it’s an existing MCP and the capacity is greater than 5MWth and less than 50MWth
- 1 January 2030 it’s an existing MCP and the capacity is equal to or greater than 1MWth and less than or equal to 5MWth
ELVs

You need to identify:
- the ELVs your plant must meet
- if your plant is exempt from meeting the ELVs
Read the guidance on complying with emission limit values (https://www.gov.uk/guidance/medium-combustion-plant-mcp-comply-with-emission-limit-values).

Apply for a MCPD environmental permit

You need to:
- select the correct permit to apply for
- complete and submit the correct form, the fee and required information
See the guidance Medium combustion plant: apply for an environmental permit (https://www.gov.uk/guidance/medium-combustion-plant-apply-for-an-environmental-permit).

Contact your regulator

England

Contact the Environment Agency.

General enquiries

National Customer Contact Centre PO Box 544RotherhamS60 1BY

Email xxx@xxx.xx (mailto:xxx@xxx.xx)

Telephone 03708 506 506

Telephone from outside the UK (Monday to Friday, 8am to 6pm GMT) xx-xxxx-xxxx

Monday to Friday, 8am to 6pm.

Wales

Contact Natural Resources Wales (https://naturalresources.wales/about-us/contact-us/general-enquiries).