The flexible foam insulation on the heat pump pipes shows exposed brass fittings and gaps at the joints. Uninsulated exposed metal causes significant heat loss to outdoor air, reducing overall system efficiency. Credit: Lawrence Leask
An On the wire story
The Heat Pump Association UK has issued new technical guidance aimed at installers working with external hydraulic pipework on monobloc air-to-water heat pumps sited outdoors within the curtilage of a home.
Endorsed by MCS, the document arrives as non-compliant insulation on external pipework remains the most common non-conformity identified in MCS audits, underlining a persistent weakness in installation quality that can affect heat retention and overall system performance.
HPA UK said the guide is designed to help installers understand why careful insulation matters, covering issues such as heat loss, pipe support and protection, wall penetrations and external trunking, as well as practical considerations including thermal conductivity, vapour diffusion, UV resistance and emissivity.
It also draws attention to the latest Approved Document Part L 2026 and includes reference images showing examples of good and poor practice. The association said the publication forms part of a wider series of installer-facing technical documents, alongside earlier guidance on control systems and residual current device selection, and encouraged installers to consult manufacturers for product-specific advice as standards and market practice continue to evolve.
Nancy Jonsson, HPA UK technical consultant, said the aim was to help ‘demystify’ the key considerations around insulating external hydraulic pipework and to improve on-site practices for better consumer outcomes.
Scott McBride, technical manager for heat at MCS, said the organisation welcomed the collaboration and remained focused on helping certified installers meet requirements and improve the quality of heat pump installations.
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