Reducing emissions in Europe’s buildings necessitates replacing fossil fuel boilers with greener alternatives. Hybrid heat pumps have been considered by some to be an interim step between fossil fuel and electric heating. ‘Hybrid heat pump’ is a term which is not well-defined, but generally understood to be a heating system which combines both fossil fuel and heat pump elements. Given the urgency of the energy transition, there is a need for a more robust body of knowledge about hybrid heat pumps.

This paper aims to provide independent analysis of hybrid systems. The authors describe the likely scenarios in which hybrid heat pumps would play a role and investigate the associated risks and benefits, including which parties bear those risks or reap those benefits.

The paper finds that only in situations where the building stock remains particularly leaky and the electricity grid inadequate would hybrid heat pumps provide some value to the energy system. This value is conditional, however, and the consumer experience necessary to facilitate it is potentially complex and costly, while providing uncertain household value in return. Much of this value can be delivered by building envelope efficiency, flexibility and other clean solutions, such as low-carbon district heating — technologies which are widely expected to be ramped up anyway.

Policymakers who are considering regulating or supporting hybrid heat pumps should ensure that these systems contribute effectively to the broader goals of reducing emissions and transitioning to a sustainable, low-cost and equitable heating sector. Recommendations include:

1. Develop a clear regulatory definition of a hybrid heat pump for policy support.
2. Decide whether the fossil fuel component of a hybrid heat pump should deliver space heating and/or hot water. This will determine what future retrofits will be needed, such as eventual emitter upgrade or installation of water storage.
3. Ensure financial and regulatory support for hybrid heat pumps is reflective of their value, noting that this is likely to be less than for standalone heat pumps.
4. Regulate and monitor hybrid systems to ensure that the heat pump component is used effectively, an optimised control strategy is in place, and emissions reductions are realised.
5. Develop a ‘needs case’ for hybrids.
6. Account for infrastructure implications (both gas and electricity) regarding a switch to hybrid systems.
7. Determine whether the electricity grid (and any planned expansion and optimisation) can cope with standalone heat pumps, and what other flexibility options are in place to support the integration of standalone heat pumps.
8. Consider any support for hybrids as part of a policy package for clean heating.
9. Temporal variability in energy market prices needs to be reflected at the billing level to ensure the flexible value of hybrid heat pumps can be achieved and that fossil fuels are used only when they will limit costs and/or emissions. Dynamic tariffs, offers and services should be widely encouraged to maximise flexibility options.