If you are planning an air source heat pump (including air-to-air systems that can provide heating and cooling), the biggest source of delay is rarely the kit. It is uncertain: do you need planning permission, do you qualify under permitted development, and what evidence should you keep if a neighbour complains or the council asks questions later?

This guide explains the current position in England, what changed in 2025, and what will change from May 2026 when MCS 020 becomes the only permitted certification scheme for permitted development. You will learn how to check your property against the limits and conditions, how the MCS 020 a) noise calculation works in plain English, and how to build a simple “permission pack” for your records.

This is practical guidance rather than legal advice. Planning rules can vary by location and can be removed by local restrictions. If you are unsure, get confirmation from your Local Planning Authority before work starts.

What changed in 2025 and why May 2026 matters

Permitted development still exists, but the conditions have changed

In England, many domestic heat pump installations can be carried out under permitted development rights, meaning you do not normally need to submit a full planning application if you meet the limits and conditions. The changes that came into force on 29 May 2025 were designed to remove common barriers, especially for homes with limited outdoor space.

The headline changes include removing the old “1 metre from the boundary” restriction, allowing larger outdoor units on houses, and widening the right so that systems can provide cooling as well as heating (provided they are not used solely for cooling). The rules also allow up to two air source heat pumps at a detached house under permitted development.

For a quick view of the official limits and conditions, use the Planning Portal guidance for air source heat pump permitted development and treat it as your checklist baseline.

May 2026: Evidence and standards become less flexible

The planning framework points to the Microgeneration Certification Scheme planning standards (MCS 020). Today, guidance refers to MCS 020 or equivalent standards, but from 28 May 2026, MCS 020 is the only permitted certification scheme. In practice, councils, installers and assessors will rely on MCS 020 documentation as the accepted method, particularly for the noise calculation evidence that underpins permitted development.

A simple way to think about it is this: 2025 removed practical barriers (space and cooling capability), and 2026 reduced ambiguity about what “compliant” looks like. If you prepare your project as if MCS 020 will be required, you reduce the risk of late surprises.

Key dates to keep in mind

29 May 2025: permitted development rules updated for domestic air source heat pumps in England.
20 September 2025: MCS 020 a) implementation date for permitted development sound calculations (as stated in the standard).
28 May 2026: MCS 020 becomes the only permitted certification scheme referenced in Planning Portal guidance.

Planning permission vs permitted development: the difference in plain English

Planning permission is an application; permitted development is a right with conditions.

Planning permission is a formal application to your council. Permitted development is a set of rights under national planning rules that allow certain types of work without making a planning application, provided you stay within the limits and conditions. Heat pumps sit firmly in this “allowed if you meet the rules” category for many homes.

Permitted development can still be unavailable in specific situations.

Even if your installation looks compliant on paper, permitted development rights can be removed or restricted. Common reasons include an Article 4 Direction, a planning condition attached to your property, or the property being within the curtilage of a listed building or a scheduled monument. Some locations also have extra siting restrictions, such as conservation areas or world heritage sites.

Treat permitted development as something you verify, not something you assume. The verification process is straightforward if you work through it methodically.

The permitted development checklist for air source heat pumps

Work through the checklist below before you commit to an installation date. If you hit a “no” on any step, it does not automatically mean the project is impossible. It means you either need a design adjustment, a different siting plan, or you should consider planning advice and potentially a planning application.

Step 1: Confirm the property type and where the unit will sit

House or block of flats: rules apply to both, but size limits differ.
Location: the unit can be on the building or within the curtilage (garden or grounds), including on a structure within that curtilage.
Roof type: installations on pitched roofs are not permitted development. Flat roofs are possible, but there is a 1 metre setback from the external edge.

Step 2: Check protected status and local restrictions

Listed building or scheduled monument: permitted development rights do not apply within the curtilage.
Conservation area or world heritage site: extra siting rules apply, particularly on walls or roofs that front a highway.
Article 4 Direction or planning conditions: these can remove permitted development rights for your property.

Step 3: Check the physical limits: size and number of units

Outdoor unit volume: for houses, the outdoor compressor unit (including housing) must not exceed 1.5 cubic metres. For a block of flats, the limit is 0.6 cubic metres.
Number of heat pumps: for a house that is not detached, only the first installation is permitted development. For detached houses, the first two heat pumps are permitted development.

Step 4: Confirm how the system will be used

The permitted development right is not intended to cover equipment used solely for cooling. Systems that provide heating and cooling can qualify, but they must not be used solely for cooling purposes. If you are considering an air-to-air heat pump for year-round comfort, the “not solely for cooling” condition is a key point to understand and document.

Step 5: Complete and retain the noise calculation evidence (MCS 020 a)

Noise is where many projects become contentious, even when planning permission is not required. MCS 020 a) sets out the sound calculation used to demonstrate that a domestic heat pump meets the permitted development noise limit. This calculation focuses on “assessment positions” near neighbouring habitable room windows and predicts the sound level at those points.

A professional survey is the easiest way to remove risk here, because you can select an appropriate unit, position it sensibly, and evidence compliance before work starts. If you are in the South West and want an installer to handle the checks end-to-end, you can request a site survey using the free survey request form.

Limits and conditions explained, with common pitfalls

Volume limits: what “1.5 cubic metres” actually means

The volume limit is based on the outdoor compressor unit, including any housing. Manufacturers often publish dimensions (height, width, depth). Multiply these to estimate the external volume. Do not rely on the “footprint” or the space it occupies on the ground. If the unit is housed in a surround or acoustic enclosure, that housing counts.

For houses, the limit is 1.5 m³, which is a substantial increase compared with older guidance. For blocks of flats, the limit is still 0.6 m³, which often pushes you towards smaller, quieter units, or careful placement to avoid needing a planning application.

How the 2025 rule changes affect siting near boundaries

The 2025 changes removed the requirement for any part of the unit to be at least 1 metre from the boundary of the curtilage. This matters most for terraced and semi-detached homes with narrow side passages, small courtyards, or gardens that are bounded closely by neighbouring land.

Removing the boundary rule does not remove your responsibility to minimise impact. You still need to site the unit to minimise its effect on external appearance and local amenity. In practice, this means you should prioritise locations that are visually discreet, avoid pointing airflow directly towards a neighbour’s patio, and manage noise and vibration.

Flat roofs: the 1 metre edge setback still applies

Even after the boundary rule removal, there is still a specific restriction for flat roofs: all parts of the heat pump must be at least 1 metre from the external edge of the flat roof. This catches out owners of extensions, garages and dormers where the only viable spot appears to be the roof edge.

If your design needs a roof-level install, consider an internal roof platform set back from the edge, or a wall mount on a rear elevation. If neither is possible, you may need to explore a planning application supported by an acoustic assessment.

Pitched roofs are not permitted for development.

Installing an air source heat pump on a pitched roof is not permitted development. If your only feasible location is a pitched roof, treat it as a planning-led project from day one and budget time for design and consultation.

Front elevations and highways: restrictions tighten in sensitive areas

The permitted development rules include siting restrictions that protect the streetscape. In conservation areas and world heritage sites, the unit must not be installed on a wall or roof that fronts a highway, or nearer to any highway that bounds the property than any part of the building. Outside those areas, you still cannot install the unit on a wall above ground floor level if that wall fronts a highway.

These rules often push installations to the rear elevation, side elevation below ground floor level, or within the garden. For many homes, that is preferable anyway because it reduces neighbour visibility and supports quieter locations.

Permitted development can be removed: what to check

Councils can remove permitted development rights through Article 4 Directions or planning conditions. Newer estates sometimes have conditions that restrict external equipment on façades. Flats may have lease restrictions. If you have any doubts, ask your local authority for written confirmation or seek pre-application advice.

Noise, neighbours and MCS 020: how to stay compliant and avoid complaints

What MCS 020 a) is trying to prove

MCS 020 a) is a calculation method that installers use to confirm whether a heat pump installation is likely to meet the permitted development noise limit. The standard is explicit that it sets out the sound calculation that must be conducted for domestic installations of heat pumps to be permitted development, and that it is designed to confirm a noise limit of 37 dB LAeq, 5 minutes at the relevant assessment positions.

This shifts noise evidence from informal “it should be fine” assurances to a repeatable method that can be checked by planning authorities. If you do not have the calculation evidence, you are more exposed if a neighbour complains later.

Key terms, simplified

Sound power level: a manufacturer’s figure that represents how much sound the unit generates, independent of distance. It is commonly used as the starting point.
Assessment position: defined as a position 1 metre outside the centre point of a neighbouring habitable room door or window.
LAeq,5mins: an average sound level over five minutes, designed to represent typical operational noise rather than momentary peaks.

How installers reduce noise risk in real homes

The most effective noise control measures happen before installation. Once a unit is fixed to a wall or slab, your options are more limited and often more expensive. A sensible design process usually includes:

Right-sizing the unit: oversized units can short-cycle, but undersized units can run harder. The goal is steady, efficient operation.
Placing the unit away from neighbour windows: moving a unit a few metres can make a material difference to the predicted sound level.
Avoiding reflective “sound traps”: tight courtyards and alcoves can reflect noise towards neighbouring openings.
Controlling vibration: anti-vibration mounts, correct fixings and a stable base reduce structure-borne noise that is often more intrusive.
Planning service access: awkward access increases the chance of poor workmanship and rattles over time.

If your property is tight on space, treat noise planning as a first-class design constraint, just like pipe runs and electrics. A survey-led approach is particularly valuable for terraces, flats, and homes with small rear yards.

When noise pushes you towards a planning application

If you cannot meet the noise limit at the relevant assessment positions, you have three main routes:

Redesign: change the unit, change the location, or use manufacturer-approved attenuation methods.
Planning application: submit a proposal with supporting acoustic evidence and siting justification.
Proceed without evidence: not recommended, as it increases neighbour disputes and enforcement risk.

A well-prepared planning application can be successful, but it is slower. For most households, redesigning early is the better option. From 2026 onwards, councils are likely to expect clearer evidence that MCS 020 has been followed, even when you are not applying for permission.

Special cases: flats, listed buildings, conservation areas and mixed-use blocks

Blocks of flats and leasehold permissions

Permitted development rights apply to blocks of flats, but the building must consist wholly of flats (not mixed with commercial premises). The outdoor unit volume limit is lower for blocks of flats (0.6 m³), and you should assume that freeholder approval and lease conditions will be as important as the planning rules.

Practical approach: treat the project as a two-track process. Track one is planning compliance. Track two is building owner approval and neighbour communication. If either track fails, the project stalls.

Listed buildings and scheduled monuments

If your property is within the curtilage of a listed building, permitted development rights do not apply for heat pump installations. That does not automatically prohibit installation, but you should expect a consent-led process. Listed building consent and planning permission are separate considerations, and you should take specialist advice early.

Conservation areas and world heritage sites

In these areas, siting rules are stricter, especially on elevations that face a highway. Many successful installations use rear gardens, internal courtyards that are not visible from the street, or discreet ground-level placements screened by planting or fencing (while still maintaining airflow and service access).

If you also need guidance for air conditioning units, see when you need AC planning permission in the UK. The principles are similar, but the permitted development details differ.

What happens from May 2026: how to future-proof your project

MCS 020 becomes the only permitted certification scheme

From 28 May 2026, Planning Portal guidance states that MCS 020 is the only permitted certification scheme for permitted development installations. The practical impact is that “equivalent” approaches become much harder to defend. If you are installing close to neighbours, or in an area where siting is sensitive, work with an installer who can show the completed MCS 020 a) calculation and keep it on file.

Questions to ask your installer before you sign

Will you complete the MCS 020, a) sound calculation for the proposed location and provide a copy for my records?
What assessment positions will you use, and how will you confirm which neighbour windows count as habitable rooms?
If the calculation is borderline, what design changes are available (unit selection, location changes, mounting method)?
What documentation will I receive at handover (commissioning, controls setup, maintenance requirements)?

You do not need to become a noise engineer. You just need to ensure the project has evidence. This is the difference between a straightforward installation and a stressful dispute later.

Building Regulations and other approvals you should not overlook

Building Regulations still apply even when planning permission does not

Planning and Building Regulations are separate. Planning is about what you are allowed to build and where. Building Regulations are about how work is carried out safely and to an acceptable standard. Planning Portal guidance states that installing a ground source or air source heat pump must comply with Building Regulations.

Many homeowners rely on a competent installer to handle notifications and compliance. If you want to understand the framework, the government overview of Building Regulations competent person schemes is a useful starting point.

Neighbour communication as a practical risk control

Most neighbour disputes start with surprise, not noise. A short conversation can remove tension, especially if the unit will be close to a boundary or if scaffolding is involved. Sharing the rough location, expected schedule, and reassurance that noise has been assessed is often enough to prevent escalation.

Practical next steps: a permission pack you can keep on file

What to collect before installation

A “permission pack” is a small folder of information that shows you have acted responsibly. It does not need to be complex, but it should be organised. Aim to include:

A one-page site sketch showing the chosen location, nearby boundaries, and neighbour windows.
Manufacturer spec sheet showing outdoor unit dimensions and sound power data.
Your MCS 020 a) noise calculation sheet for the chosen location.
Photographs of the location before work starts (useful if landscaping changes later).
Notes on any local restrictions checked (conservation area, listed status, Article 4, planning conditions).
Installer quotation and scope, including mounting method and vibration control.

What to keep after installation

Commissioning and handover records, including control settings.
Any maintenance requirements and service intervals.
Warranty documentation and contact details for support.

When to get help

If you are still deciding whether your property qualifies, or you want a survey-led recommendation on siting and compliance, speak with a specialist before you commit. You can use the Controlled Climate contact page to discuss your project or ask a specific planning-related question.

Summary

The 2025 changes made it easier to install domestic air source heat pumps under permitted development by removing the 1 metre boundary restriction, allowing larger outdoor units on houses, and supporting systems that can heat and cool (as long as they are not used solely for cooling). From 28 May 2026, MCS 020 becomes the only permitted certification scheme referenced in Planning Portal guidance, so evidence and documentation matter more.

Use the permitted development checklist to confirm your property type, siting constraints and protected status.
Treat noise assessment as a design constraint. Ensure the MCS 020 a) sound calculation is completed for the proposed location and kept on file.
Avoid common pitfalls such as pitched roof installs and flat roof edge placement.
Keep a simple “permission pack” (sketch, spec sheet, noise calculation, photos, restriction checks) to reduce dispute and enforcement risk.

Frequently Asked Questions

Do I need planning permission for a heat pump in England?

Often no, provided you meet permitted development limits and conditions. If you fail any condition (for example, pitched roof install, listed building curtilage, or siting restrictions), you may need planning permission or specialist consents.

What exactly changed on 29 May 2025?

The key changes include removing the 1 metre boundary restriction, increasing the allowable outdoor unit size for houses, and widening the right to cover heating and cooling systems that are not used solely for cooling. Detached houses can install up to two units under permitted development.

What is MCS 020, and why does May 2026 matter?

MCS 020 is the planning standard referenced for permitted development heat pump installs. Planning Portal guidance states that from 28 May 2026, it will become the only permitted certification scheme, reducing reliance on “equivalent” approaches.

Is the noise calculation only needed if a neighbour complains?

No. The safest approach is to complete the MCS 020 a) calculation before installation and keep it on file. It also helps you choose a position that is less likely to cause issues.

Can I install a heat pump on my flat roof?

Potentially, but all parts of the unit must be at least 1 metre from the external edge of the flat roof. Installations on pitched roofs are not permitted development.

Do Building Regulations apply if I do not need planning permission?

Yes. Planning and Building Regulations are separate. Work must still comply with Building Regulations, and installers often manage notification through competent person schemes.

Heat Pump Planning Permission in England: 2025 Rule Changes and What Happens from May 2026 (MCS 020)