07 May 2026
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The Department for Energy Security and Net Zero declared the issues with sub-standard and poorly installed insulation, which is already costing heat pump households approximately £74 a year in avoidable heat loss - or £20 million in wasted energy across affected heat pump households, annually.
The DESNZ admission was made at the Chartered Institution of Building Services Engineers (CIBSE) Decarbonisation Conference in London, to an audience of hundreds of leaders and practitioners from across the built environment.
To protect households from avoidable heat loss, WattsWatt - the UK’s national energy service created to unlock heat hours for households across Great Britain - has launched a free support service to help heat pump households check whether their external
2 See footnote 1 1 Annual cost of 90% of heat pump households (270,000) losing 5% heat - £74 per household.
pipework has been properly insulated. Households can also enter in the length of their external pipework to understand the annual heat loss.
Data analysts from WattsWatt have calculated - based on the government’s annual target of installing 400,000 heat pumps a year between now and 2030 - that heat pump households will lose £82 million a year if external pipe insulation issues are not fixed.
Lisa Malyon, Co-founder and CEO of WattsWatt, said: “It’s quite straight-forward - if your external pipes aren’t insulated properly, the water cools as it travels through these outdoor pipes, affecting the temperature inside the house. To get the house back up to temperature, the heat pump has to work harder, which uses more energy.
“We first became aware of the issue when households complained their heat pump had stopped working - saying it was nowhere near as good as it had been when it was first installed. It turns out, their external pipework had been insulated with basic grey insulation designed for inside - and it was soaked through.”
Professor Richard Fitton, Professor of Building Performance at the University of Salford, comments WattsWatt’s heat pump check tool: “Heat pump technologies need careful design and installation for optimum performance. We are experimenting in the Energy House Labs to understand the heat losses associated with inferior external pipe insulation and will update on that soon.”
Chris Ridge of the Thermal Insulation Contractors Association (TICA) said: “Our latest white paper has established thermal insulation of pipework as a low-hanging fruit for decarbonisation. In the battle to win public trust for heat pump technologies we simply cannot afford the additional energy losses caused by incorrectly specified and installed thermal insulation on external pipe runs.
“The new WattsWatt campaign is helping to highlight a key issue that has otherwise remained under the radar for too long.”
Lisa Malyon continues: “This avoidable issue risks undermining confidence in heat pumps unnecessarily. When households experience higher bills or lower comfort, the heat pump itself is often blamed, but in many cases it is not the technology - it is the installation detail.
“There’s a critical information gap for installers. The Microgeneration Certification Scheme’s MIS 3005-I installation standard doesn’t specify what type of insulation should be used outdoors. Instead, MCS refers installers to the heap pump manufacturers’ instructions, however these do not tend to specify what insulation is required either.”
Consumer rights
Households are encouraged to carry out a simple visual check of their installation at https://wattswatt.co.uk/heatpumpcheck, looking for exposed or uninsulated pipework, gaps or thin insulation, damaged lagging, poorly sealed joints or pipework left exposed to weather conditions. Where issues exist, consumers are encouraged to contact the installer and request an insulation upgrade. If concerns are not addressed, consumers are protected under the Consumer Rights Act 2015, which requires installations to be carried out with reasonable care and skill and to be fit for purpose.
More information can be found at www.wattswatt.co.uk.
