Compliance with the updated MCS 020 standard became mandatory on 20 September 2025 for installers seeking to install air source heat pumps under Permitted Development, MCS has confirmed. The standard was published on 20 March 2025 following a consultation in January 2024 and a consultation response in November 20241.
The update was driven by government amendments to Permitted Development Rights (PDR) applying in England, which MCS lists as: removal of the 1m boundary rule, enabling heat pumps to be installed within 1m of the property boundary; an increase in the size limit of the heat pump for dwelling houses from 0.6m3 to 1.5m3; a doubling of the number of heat pumps permitted, from one to two for detached dwelling houses; and support for the rollout of air-to-air heat pumps that can also provide a cooling function1.
"Compliance with this update is mandatory for installers seeking to install air source heat pumps under Permitted Development from the date of implementation, 20 September 2025."
The standard has been split into two parts: MCS 020 (a) for air source heat pump sound calculation and MCS 020 (b) for small wind turbine sound calculation. MCS states there are no changes to the requirements for small wind turbines1. MCS will hold the A-weighted sound power level for MCS certified products on the MCS Product Directory, a figure to be determined by manufacturers at the same conditions as the Eco Design Directive, with guidance to clarify those conditions1.
MCS has also clarified what can and cannot be considered a solid barrier, how to determine the assessment position, what can and cannot be considered a reflective surface, and the definition of a habitable room1. A methodology will be introduced for including up to two air source heat pumps in the MCS 020 (a) sound calculation, and installers will be offered options for completing the calculation, including the current paper-based method and an Excel tool. The Excel tool will also be capable of completing the sound calculation for up to four air source heat pumps, for those installing under full Planning Permission1. Working with DESNZ and other industry stakeholders, MCS will develop a guidance document for installers on installation noise mitigation measures for air source heat pumps1.
| Change | Detail |
|---|---|
| Boundary rule | Removed; installation within 1m of the property boundary enabled |
| Size limit (dwelling houses) | Increased from 0.6m3 to 1.5m3 |
| Number permitted | Doubled from one to two for detached dwelling houses |
| Air-to-air heat pumps | Rollout supported, including cooling function |
Compliance with MCS 020 (a) under PDR applies irrespective of whether the installation is MCS certified or not1.
Why it matters for households
The sound calculation sits behind the Permitted Development Rights for Home Energy Equipment that let many homes install an air source heat pump without a full planning application. The MCS 020 noise assessment determines whether a proposed unit meets the noise condition attached to those rights, so the changes affect where a unit can go, how large it can be and how many can be fitted. Households weighing up an installation will encounter the standard through the Heat Pump Standards, Testing and Certification that installers work to, and through the installers who must demonstrate compliance. The removal of the 1m boundary rule and the larger size limit widen the range of properties where a permitted development route may be available, which matters most for homes with limited external space. The requirement applies whether or not the installation is MCS certified, so the noise assessment is not confined to certified work.
What happens next
MCS states that the updated standards and the Excel calculation tool are available through its Standards and Tools Library, and that queries should be sent to its meetings address1. The guidance document for installers on installation noise mitigation measures is to be developed with DESNZ and other industry stakeholders; no publication date for that document is given in the announcement1.
Sources1 cited
- MCS has published an updated version of MCS 020 - MCS, mcscertified.com