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Automating heat pump flexibility: results from a pilot


HeatFlex UK: a collaboration between CNZ and Nesta


As we move to a fully electrified energy system, it is well understood by policymakers, regulators and businesses across the energy sector that using energy more flexibly will be necessary to manage the grid. Individual consumers will play a critical role by changing how and when they use electricity, resulting in ‘intelligent demand’. 

In the short to medium term, the two biggest sources of consumption from households are likely to be from electric vehicles and heat pumps. Improving our understanding of the potential to use these technologies flexibly is key to the design of the changing energy system.


Centre for Net Zero partnered with innovation agency Nesta on HeatFlex UK: a project to pilot and develop a trial to investigate heat pump flexibility, consumer preferences and how these are affected by third-party automation and pre-heating.

We ran a small-scale pilot between February and April 2023 which we used to test and refine a heat pump flexibility intervention. We remotely took control of participants’ heat pumps for short periods of time, which we refer to as ‘events’. Our aim was to reduce their electricity consumption during a two-hour period, while ensuring participants stayed warm and comfortable by ‘pre-heating’ their home for 2 hours before the peak energy demand period began.

HeatFlex intervention

Schematic which shows how the HeatFlex intervention works in theory. Our pilot explored how implementing this worked in practice.

HeatFlex UK uses a mixed methods approach, incorporating data science, behavioural science and design-led user engagement methods to understand what influences the flexibility potential of heat pumps in homes. 

Key Findings

The findings and provisional conclusions from our pilot come with the strong caveat that our sample size was too small to support generalisable conclusions. 

Flexibility potential

  • We found indicative evidence that we were able to move electricity consumption to different points in the day. 
  • We did not find evidence that days with HeatFlex events had different total electricity consumption to days without an event.
  • Differences in participants’ arrangements of their home may have affected the magnitude of demand reduction.

Acceptance of third party automation 

  • 9 out of 10 participants reported that the automation of their heating was acceptable.
  • There were eleven instances where participants opted out during events – mostly due to feeling too cold. This does not suggest the automation itself was driving opt-out. 
  • Participants were less accepting of morning events than afternoon events – indicating that we may need different demand shifting strategies depending on the time of day. 

Participant thermal comfort

  • Participants’ self-reported comfort ranges differed drastically in some cases, with a maximum range of 10°C and a minimum range of 2°C.
  • The majority of temperatures that participants self-reported at the end of the pre-heating window were greater than their normal setpoints – suggesting broadly that pre-heating ‘worked’. 
  • Temperatures generally decreased during the flexibility window by 0.3°C on average from start to end. 
  • Participants generally reported that their thermal comfort did not change between the start and the end of the flexibility window.

Next Steps 

We intend to run a larger trial in winter 2023-2024 which should deliver more robust results. One of the limitations of the pilot was that we were constrained in our ability to make any causal claims about the effect of our intervention. The larger-scale HeatFlex UK will be a randomised controlled trial, which will overcome this issue. 

Related work

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Quantifying Demand Flexibility: Towards a Standardised Approach to Baselining
Outlining a potential set of common principles for quantifying demand flexibility, considering the value of different methods and calling for a standardised approach to baselining in future. A collaboration between Centre for Net Zero, Enedis, Enel X and National Grid Electricity Distribution and Octopus Energy.
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Estimating the impact of last winter's Demand Flexibility Service (DFS) on energy demand and economic welfare, and measuring the impact of changing notification period and incentive level on demand reduction.
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The ‘Smart Building Rating’: a digital tool to scale demand flexibility
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Automating heat pump flexibility: results from a pilot
HeatFlex UK: a collaboration between CNZ and Nesta
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Insights from the UK's largest consumer energy flexibility trial
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