29
.
July
,
2026

Heat Pump Permitted Development 2026: How AI-Assisted Siting Gets You Under MCS 020

Written by
Stefano Fonseca
Stefano Fonseca
Freelancer

Stefano Fonseca is an AI visibility specialist for companies with impact. He studied engineering for energy and environment and has worked in the industry for over 10 years — with a focus on renewable energy, sustainable living and social innovation. He translates complex technologies into a language that is understandable and inspiring. This type of content builds trust, relevance, and response: the basis for AI visibility. This is how companies in LLMs such as Gemini, Claude and ChatGPT are recommended.

‍

In this article
Just try it out for yourself.
Try it now

From 28 May 2026, a single standard decides whether a heat pump job skips planning permission in England: MCS 020. Miss the 42 dB(A) noise limit and a straightforward install becomes an eight-week planning application. Getting the outdoor unit's position right — before the site visit — is now a commercial skill, not an afterthought.

🔍 Key takeaways

  • From 28 May 2026, MCS 020a is the only certification scheme accepted for heat pump permitted development in England.
  • MCS 020 caps outdoor-unit noise at 42 dB(A), measured 1 metre from a neighbour's habitable room window.
  • England scrapped the one-metre boundary rule in 2025 and raised the unit size limit to 1.5 cubic metres.
  • AI-assisted siting lets installers test the unit's position against the noise limit before quoting the job.
  • A failed noise assessment forces a full planning application: eight weeks and a £258 fee in England.

What changes for heat pump permitted development in England in 2026?

From 28 May 2026, MCS 020a becomes the only certification scheme England accepts for air source heat pumps installed under permitted development, and the previous 'equivalent standard' route closes. MCS 020a has been mandatory for every permitted development install since 20 September 2025. Compliance is no longer optional paperwork, it is the gate to skipping planning permission.

The tighter certification rule arrives alongside a wider opening of permitted development. The Town and Country Planning (General Permitted Development) (England) (Amendment) Order 2025, in force from 29 May 2025, scrapped the one-metre boundary rule, raised the size allowance, and let detached homes take a second unit.

ConditionBefore 29 May 2025From 29 May 2025
Distance from boundaryMinimum 1 metreNo minimum distance
Max outdoor unit volume (house)0.6 m³1.5 m³
Units per detached houseOneUp to two
Air-to-air (cooling) unitsExcludedIncluded
Noise certificationEquivalent schemes allowedMCS 020a only (from 28 May 2026)

What is MCS 020, and how does the noise calculation work?

MCS 020 is the MCS planning standard that predicts how loud an air source heat pump will be at the nearest neighbour's window. The installer takes the manufacturer's declared sound power level, applies corrections for distance, reflections and barriers, and calculates the sound pressure level one metre from the centre of the nearest neighbour's habitable room window.

The threshold is fixed: 42 dB(A) or below qualifies for permitted development; anything higher needs a full planning application. The standard assesses against an assumed background level of 40 dB(A). In March 2025 MCS split the standard into MCS 020a for air source heat pumps and MCS 020b for small wind turbines.

Which siting conditions decide whether an installation qualifies for permitted development?

Beyond the 42 dB(A) noise limit, several siting conditions determine whether a heat pump keeps its permitted development rights in England:

  • Outdoor unit size: The compressor unit, including its housing, must not exceed 1.5 cubic metres on a house or 0.6 cubic metres on a block of flats.
  • Number of units: Detached houses may have up to two units under permitted development; semi-detached, terraced homes and flats are limited to one.
  • Position in conservation areas: The unit must not sit on a wall or roof fronting a highway, nor closer to a highway than the building itself.
  • Listed buildings: Permitted development does not apply. The job needs planning permission and listed building consent, whatever the noise result.
  • Siting for amenity: Units must be positioned to minimise their effect on the amenity of the area and removed when no longer needed.

How does AI-assisted siting help installers pass MCS 020?

AI-assisted siting lets installers test a unit's position against the 42 dB(A) limit before anyone visits the property. By modelling the outdoor unit, the neighbour's nearest habitable window, distances and any barriers digitally, the software runs the MCS 020 calculation across different positions and shows which ones keep the job inside permitted development.

autarc's installation simulation places the outdoor unit against the property and the nearest habitable window, then tests distances and barriers against the MCS 020 threshold. Installers see whether a position passes before committing to a design.

In practice, AI-assisted siting reshapes the quoting workflow into four steps:

  1. Capture the property: A digital model or scan records the building, boundaries and the neighbour's nearest habitable window.
  2. Place the unit: The installer positions the outdoor unit and any acoustic barrier in the model.
  3. Run MCS 020: The software calculates the predicted sound pressure level and flags whether it clears 42 dB(A).
  4. Decide the route: A pass confirms permitted development; a fail signals a full planning application before the quote goes out.

What happens when a heat pump can't meet MCS 020 under permitted development?

When the predicted noise exceeds 42 dB(A), or the unit breaks another permitted development condition, the installation needs a full planning application. In England that means an eight-week decision period and a £258 householder fee, with no guarantee of approval. Listed buildings need planning permission plus listed building consent regardless of the noise result.

RouteWhen it appliesFeeTimeline
Permitted developmentMCS 020 pass and all conditions metNo planning feeImmediate
Full planning applicationNoise above 42 dB(A) or a condition breached£2588 weeks+
Planning + listed building consentListed building£200–£5008–12 weeks

Conclusion: The noise number now decides the job

From 28 May 2026, MCS 020a is the single gate to permitted development for heat pumps in England. The variables that decide it — distance, barriers, the neighbour's window — are siting choices, not fixed facts. Installers who model them before the site visit protect both their timelines and their margins.

Test the siting before you quote with autarc

Getting the siting right before the site visit is where MCS 020 compliance is won or lost. autarc brings heat loss calculation, installation simulation and construction documentation into one heat pump planning workflow — so installers can test the noise result, confirm permitted development, and quote with confidence. Book a free demo and an autarc team member will show you the platform live.

‍

💬 Frequently asked questions

Does MCS 020 apply to heat pumps in Scotland and Wales?

No, MCS 020 governs permitted development in England. Scotland and Wales set their own planning rules and permitted development limits, so installers working across borders should check the relevant national guidance before assuming the 42 dB(A) route applies.

Do ground source heat pumps need an MCS 020 assessment?

No, MCS 020a covers air source heat pumps, whose outdoor units produce the noise the standard measures. Ground source systems have no external compressor unit of the same kind, so the sound calculation does not apply in the same way.

Which sound power figure should installers use in the calculation?

The manufacturer's declared sound power level for the specific model, taken from its technical data. Using a generic or optimistic figure risks a calculation that fails on site or misrepresents the installation to the local authority.

Does a garden fence or wall count as a barrier in MCS 020?

It can, if it sits between the unit and the neighbour's window and meets the standard's requirements. A solid barrier lowers the predicted sound pressure level, which is why siting the unit behind an existing structure often moves a marginal job to a pass.

Is a second heat pump on a detached house always permitted development?

Not automatically. Detached houses may have up to two units under the 2025 rules, but both must still meet every condition — including the noise assessment and the 1.5 cubic metre size limit.

Does MCS 020 apply when replacing an existing heat pump?

Often, yes. A replacement that changes the unit or its position should be assessed against current permitted development conditions, including MCS 020, rather than relying on the original approval.

What records should installers keep for an MCS 020 assessment?

The completed sound calculation, the manufacturer's sound power data, and the siting details used. These evidence permitted development compliance if a local authority or an MCS audit queries the installation later.

How long does a full planning application take if MCS 020 fails?

In England, a householder application carries a statutory eight-week decision period, though many authorities take 8 to 13 weeks in practice. A refusal can add months and a resubmission.

References

  • Air Source Heat Pumps: New Permitted Development Rules – Logic4training, accessed 29 July 2026, logic4training.co.uk
  • Heat Pump Permitted Development 2026: Planning Rules England – Cucumber Eco, accessed 29 July 2026, cucumbereco.co.uk
  • Heat Pump Planning Permission England (2025) & May 2026 MCS 020 Rules – Controlled Climate, accessed 29 July 2026, controlled-climate.co.uk
  • Listed Building Heat Pump UK Guide 2026 – ASHPCost, accessed 29 July 2026, ashpcost.co.uk
  • MCS 020 Now Mandatory for Heat Pump Planning – UKEM Group, accessed 29 July 2026, ukem.co.uk
  • New Permitted Development rules in England: air source heat pump installations must now comply with MCS 020 a) – MCS, accessed 29 July 2026, mcscertified.com
  • New UK planning rules for heat pumps come into effect – pv magazine, 2025, pv-magazine.com
  • Planning Permission: Air source heat pump – Planning Portal, accessed 29 July 2026, planningportal.co.uk

Book a demo now and get started.

Book a demo