HPA UK publishes MCS-endorsed guide on insulating external heat pump pipework

Heat Pump Association UK (HPA UK) has published guidance for installers on insulating the external hydraulic pipework of monobloc air-to-water heat pumps, at a time when it says non-compliant insulation is the most common non-conformity found on MCS audits.

The document, launched on 7 October, is endorsed by MCS and covers monobloc units sited outdoors within the curtilage of a home. HPA UK said it is the latest in its series of technical documents written for heat pump installers.

Nancy Jonsson, HPA UK Technical Consultant, said: "HPA UK are keen to continue to support installation businesses to better understand regulations and standards."

HPA UK said the guide aims to help installers understand why insulating the outdoor pipework of a domestic monobloc system matters in cutting system heat losses and supporting overall efficiency.

What the guide covers

According to HPA UK, the document sets out good practice for insulating external pipework, clipping insulated pipes, insulating and sleeving pipework where it passes through walls, and using external plastic trunking.

It explains the common characteristics of external pipework, including thermal conductivity, water vapour diffusion factor, UV resistance and emissivity factor. It also summarises the relevant parts of Approved Document L 2026 and includes reference images showing good and poor practice.

The 2026 edition of Approved Document L, published by the Ministry of Housing, Communities and Local Government, supports Part L of Schedule 1 to the Building Regulations 2010 and is issued in two volumes, covering dwellings and buildings other than dwellings. GOV.UK says earlier versions continue to apply to buildings subject to previous regulatory standards.

HPA UK said the guidance does not cover flats, multi-occupancy buildings, high-rise dwellings or commercial buildings, and that for those cases installers should seek advice from a specialist thermal insulation contractor. It added that the document is for general information only and does not replace regulatory or manufacturer requirements.

MCS involvement

Scott McBride, Technical Manager for Heat at MCS, said: "MCS is proud to have worked with HPA UK on developing this guidance document for heat pump installers." He thanked the MCS Heat Pump Working Group for its contribution and said MCS remained committed to supporting certified installers in meeting its requirements and improving outcomes for consumers.

The guidance arrives in a growing market. MCS recorded more than 60,000 certified heat pump installations in 2025, the most in a single year, and said the Boiler Upgrade Scheme funded nearly half of all heat pumps installed that year.

Earlier guidance

The pipework document follows a run of installer-focused publications from the association. A Control Guide for Air-Water Heat Pump Systems, produced jointly with BEAMA and announced on 11 November 2024, was prompted by a high number of enquiries about how to interpret Approved Document L on single-zone versus multi-zone systems.

In February 2025 the association launched annual service checklists for air, ground and water-to-water heat pumps, developed by its Technical Working Group. It has also published Guidance on Residual Current Device Selection for Heat Pumps. HPA UK said all its guides are free to download from its website, where the new document is listed as External Pipework Insulation Guidance alongside 11 other technical resources.

HPA UK describes itself as the united voice of the heat pump sector. In the release it said it represents more than 450 organisations, with members accounting for about 90% of heat pumps sold in the UK. HPA UK is the trading name of HPA Ltd.

The association said it expects to keep reviewing and updating all its guidance documents as standards and practices evolve.