The emphasis on systems approaches (see section 2.3 for a brief explanation of what we mean by this term) in an transdisciplinary analysis may seem ad hoc, but there are a number of intersecting reasons why it is a reasonable place to start. One reason lies in recent philosophical developments to connect the sustainability-science focused work of the Zurich school of transdisciplinary research (Lang et al., 2012) with systems thinking and practice modelling tools (Morgan et al., 2025). These developments also sit well with recent programmes of work to support more “systems thinking” in the UK government (HM Government, 2023; Royal Academy of Engineering, 2023). However these latter, policy-focused efforts emphasise the systematic aspects paying limited or no attention to the transdisciplinary context into which these approaches potentially gain important impacts. Given the plurality of complex and wide-ranging challenges that UK and other countries currently face, including climate change, international conflicts and a shifting world order, we consider that this study comes at an important moment for the topic and provides a useful synthesis and call to action. At the same time, it is important to consider

In part our goal is to test not the validity of ‘transdisciplinary engineering’ here, but rather whether the addition of systems approaches are worth considering. Therefore, the key focus for this paper is to justify the systems emphasis, more than the transdisciplinary basis. A key reason why the null hypothesis might be true (that is, that systems approaches are not fundamentally useful in policy analysis) is that systems ideas are ones promoted by engineers (see Royal Academy of Engineering, 2023). It is therefore possible that systems approaches have been promoted by some (typically, systems) engineers simply because it is one of the tools they are familiar with, and not because systems concepts play an important role in understanding national policy planning choices.

One way to assess the robustness of our hypothesis within the confines of this paper is to explore two comparable cases: one a contemporary case in sustainability decision making where policy is failing (and where the absence of systems approaches and transdisciplinarity might therefore be visible) and a documented historical case (from which success or failure can be established) analysed from non-engineering perspectives, that is close enough geographically and by economic sector to enable valid learning for the contemporary case. Given the focus of the special issue, and the core knowledge of the authors, we have settled on comparative UK cases within the energy sector. This links to the sustainability theme as current policy goals in UK energy are strongly focused on carbon reduction in response to the climate crisis.

A key challenge within these efforts is the decarbonisation of UK home heating, where special emphasis has been placed on replacing natural gas boilers with electric-based heat pumps in over 20 million homes. The comparative case is also in the UK, but from 60 years earlier where a similar scale of change was executed in the shift from the incumbent ‘town gas’ used for heating and cooking to newly-discovered natural gas supply. This historical ‘transition’ (as the authors of the papers we draw from frame it) has been subject to two separate case study analyses by social science scholars from different traditions, representing a useful and manageable case for exploring if evidence of what is now recognised as transdisciplinary engineering and systems approaches emerge in this case when analysed by non-engineers. Further, this case is useful because there are clear indications of success (completion of the transition). The logic here is that if transdisciplinary and systems approaches do emerge, this provides some validation that such an approach has a wider merit than simply being useful to engineers. If so this can serve as a reasonable basis to further explore the application of this in the contemporary policy setting of accelerating heat pump uptake.

In the rest of this paper, we introduce and discuss engineering policy and theories on transdisciplinary engineering and systems approaches in detail and add to our hypothesis in section 2. Having introduced the theoretical framework, in sections 3 and 4 we then use previous research to explore two case studies of past and current transitions to UK domestic heating and consider the potential of transdisciplinary engineering in these contexts. In section 5 we highlight the lack of transdisciplinary systems approaches in current policies for the shift to low carbon heating. In section 6 we highlight two examples of visualisation tools and provide a summary of how the principles we have been discussing could apply to the low carbon heating transition. Finally in section 7 we discuss our findings and conclude the paper.

The concept of ‘engineering policy’ is meant to capture both ‘policy for engineering’—the way a nation manages or governs its engineering capacity—and ‘engineering for policy’—the use of engineering skills and knowledge to advise policy design and development—in the same way ‘science policy’ refers to both policy for science and science for policy (Cooper et al., 2023). While both senses are inter-related, we are focused more specifically on engineering for policy here, and in particular aim to explore how engineering (a collection of technical disciplines and practices) can be effectively deployed into policy design spaces that are less technical and more social and political in nature. Previous research by Liote (2022) and Cooper et al. (2021)—which are rare examples of empirical studies on engineering advice to policy in practice—emphasised the importance of effective collaboration between those in government trained as engineers and those not. The studies identified this as a key component of transdisciplinarity and also revealed a wider lack of frameworks for understanding how to best shape these interactions effectively.

While in this paper we focus on transdisciplinary and system approaches, at the same time we recognise that there are other variations which aim to bring engineering into wider areas of action, beyond the typical places of construction, manufacturing, technical design and so on. For instance, the related field of ‘transition engineering’ offers an alternative and interesting framing. Transition engineering is:

Space limitations prevents a more detailed appraisal here but the positioning of transition engineering draws on lessons from safety engineering and therefore may be understood as tackling problems within engineering (and the way engineering is carried out) as opposed to understanding how ‘engineering thinking’ may usefully be applied in policy analysis settings. Indeed, it is highly likely that developments in transition engineering may help a better application of engineering-based methods in policy in the future since any transition engineering methods are likely to fit better into the wider needs of policy analysis. We do, however, return briefly to lessons from transition engineering later in the paper in section 7.

Transdisciplinarity is an emerging cultural, philosophical and epistemic shift in the contemporary practice of science which builds on interdisciplinarity—the integration of knowledge and methods across disciplines (Barry and Born, 2013). It also connects to the idea of ‘co-production of research’, where academic and non-academic actors collaborate to shape knowledge production for action (Edelenbos et al., 2011). As developed most recently in the field of sustainability science, transdisciplinarity has been defined as:

The emphasis throughout Lang et al.’s seminal paper is on integration of knowledge across different disciplines (i.e., interdisciplinarity) and between academia and practice communities, with this definition supported by a recent handbook on transdisciplinarity (Lawrence, 2023). Interestingly, the engineering design community also recognises the need to collaboratively and systematically develop products, their patterns of use and the institutional structures in the which they operate (e.g., Reich and Subrahmanian, 2022) reflecting a natural transdisciplinary orientation within (at least one field of) engineering.

Finally, as noted above in the section on engineering policy—specifically, engineering for policy (engineering advice)—this is the type of setting where a transdisciplinary approach is considered most important. The definition above aligns well with ones offered in the transdisciplinary engineering literature too, for example Wognum defines as transdisciplinary engineering research as:

Across all these different definitions, a key concept is central to transdisciplinary practice—it involves the collaboration and/or integration of ideas and practices across different knowledge communities. This typically includes between physical scientists, social scientists and community or policy actors (typical of transdiscplinary research) or between engineering researchers, social scientist and business actors (typical of transdisciplinary engineering). Bringing engineer and engineering approaches into policy settings is one of the relatively unusual elements of our approach here, one that is closely allied to the engineering policy framing set out at the start of this paper.

This makes transdisciplinary engineering particularly suited to applications in policy decision-making for sustainability. However, a practical challenge emerges for those wanting to deploy this in policy settings as noted above—that is, the challenge of integrating a range of different perspectives under pressure of limited time and resources. Given the different orientations of policy and research (explored by Cooper in the energy sector, 2018) this creates a need to explore specific mechanisms to enable transdisciplinary engineering to be effectively applied in policy. Usefully, Morgan et al. (2025) build out a significant amount of philosophical architecture around these issues, and conclude that the use of systems approaches (or “systems thinking” as they and many others term it) can better co-ordinate and integrate different perspectives simply and coherently. We build on their work here—rather than repeat it—with the goal of exploring both the validity of systems approaches and its practical application to a live case. We next consider what we mean by systems approaches.

Since general system theory was developed in the second half of the 20th century, it has been applied to numerous fields. ‘Hard’ system theory, sees systems as interconnected elements which can be controlled, whereas ‘soft’ systems acknowledge the validity of subjective experience (Zexian and Xuhui, 2010). Collectively this can be called a ‘systems approach’—something that has been applied in multiple ways in sustainability and climate change policy arenas, including in the UK (e.g., HM Government, 2023). System approaches can be defined as:

A systems approach covers a range of methods that share a core set of concepts (Arnold and Wade, 2015). Our interest in systems approaches at this point is in first characterising them sufficiently to understand whether ‘systems’ concepts are visible within non-systems analyses of an historic case study. We do this to validate the claim that systems approaches are fundamental to effective sustainability decision-making but also as a basis for understanding how systems approaches can be practically implemented in policy decision-making.

Drawing on a synthesis and review of systems approaches by Arnold and Wade (2015) we briefly present one set of elements for understanding and deploying a systems approach. These seven elements¹ help orient a practitioner, engineer, social scientist or any other relevant stakeholder to the systemic nature of the issue they are confronting.

Again, due to space limitations we do not explore this list in depth but rather use it as a typical example in which systems approaches are turned into practical guidance. The point here is to first ask whether we can identify the presence of these elements in non-systems analyses of an historic case relevant to a related contemporary case. If so, this provides evidence that systems approaches, even if not deployed by systems specialists, may in some sense be intrinsic or otherwise foundational features of policy challenges that demand better sustainability decision-making.

Arapostathis et al. (2019) take a transitions management approach to analysing the switch to natural gas. Transitions management (Loorbach, 2010) is a political science approach to understanding transitions and focusses on the role of governance and institutions in enabling transitions. For these purposes transitions are defined as:

In line with this approach, they highlight that the gas transition took place in a much more centrally managed economy than that of the UK today and began with the dismantling of multiple individual town gas companies and the creation of state-owned British Gas which nationalised and consolidated the industry, providing centralised control of the transition. They note the contrast with today’s industry which:

Arapostathis et al. also highlight the importance of a ‘Fordist’ approach to organisation—following the industrial manufacturing approach to standardising products and processes developed by Henry Ford in the early 1900s—to reduce uncertainties, leverage economies of scale and exercise control over the numerous contractors who carried out the installation work. An 8–9-week formal training programme with harmonised technical examination processes was required for all contractors and was administered by 13 new training and examination centres, there were also clear expectations in terms of manner and approach. These requirements were facilitated by a skilled workforce seeking jobs at that time and the transition was supported by substantial resources dedicated to rapidly dealing with any complaints.

This highlights one of the seven elements of systems—understanding system structure. The authors focus on this, and importance they give to it, reinforces the idea that system structure is an important way of understanding how a transition—in their terms—happens.

The transition was compulsory, with town gas being cut off to homes on a given date. Technicians were also given authority to force entry into buildings to switch the technology at the appropriate time for each area if permission was not forthcoming, something that would be close to unthinkable today. Conversion of essential appliances took around 10 h (i.e., was completed in 1 day) and non-essential appliances were converted in the following few days. This command-and-control strategy was also supported by incentives such as the switch being cost free to households, with free conversion—or where necessary replacement (usually if more than 14 years old)—of their own existing appliances to work on the new fuel and with a free call back for up to 8 weeks post switch to deal with any problems, which at the height of the process was needed in around 25% of cases.

In addition, an aggressive, centrally directed public relations and education campaign was developed for the ‘high-speed gas’ and new ‘modern’ appliances, including local public events, leaflets, talks and even film screenings on the benefits of natural gas and its strategic priority for the UK. Another initiative was live cooking demonstrations from ‘home economics graduates’ comparing the two gas types and showing ‘the enhanced safety, convenience and evenness of cooking with natural gas’ (Arapostathis et al., 2019, p. 132), while standardised ‘bake tests’ were also sometimes conducted during call back visits to help support households with learning and to check that appliances were functioning effectively. This included specific guidance to Jewish and Muslim households on ensuring even cooking of Hallal and Kosher food.

Agreement was made with multiple appliance manufacturers and suppliers that they would develop conversion sets for their own appliances and that they would only sell multi-gas type appliances from the 1st of April 1968. Arapostathis et al. also highlight the Gas Councils’ generally harmonious and positive relationship with the various governments of the day, both Labour and Conservative, and how they enjoyed mostly steady government support and backing throughout the transition.

It can be seen that this was therefore a purposeful, planned and centrally managed transition with strong and consistent government support in a very different structural context to today’s environment. It points to the range of approaches and expertise used in creating functional outcomes for households, which contributed to the rapid progress recorded. This suggests the need to ensure that any co-ordination within the system recognises the role of diverse actors in ensuring two key elements: (i) its resilience to failure and (ii) ability to self-correct, something which is also highlighted in the second paper discussed below. Notably the designers of the approach acknowledged this and put transparent complaint and redress processes in place to handle problems, demonstrating how awareness of distinct roles and benefits of specifically designed functions can support the system effectively. This aspect of their analysis reveals a strong flavour of recognising the importance of interconnections between elements in the system. These interconnections (and the recognition of them) seems to form a key basis for effective action to carry out the transition successfully.

We now look at another angle on this historic case, taken from a paper by Hanmer and Abram (2017).

Hanmer and Abram (2017), analyse the same town gas to natural gas case, again framed as a ‘socio-technical transition’ using Actor Network Theory (ANT)—a social theory first developed by Latour (2007) and others. This is therefore from a quite different social theoretic approach from transition management with a distinct, scholarly community, if albeit still within the broad disciplinary grouping of social sciences.

Hanmer and Abram highlight the importance of the “actor networks” comprising both people (including installers, manufacturers, designers, regulators and so forth—although strangely not households!), and technical system components [such as gas drilling, national distribution pipework, household appliances, etc. (Hanmer and Abram, 2017)]. As with the previous paper they acknowledge the centralised control, management and state sponsoring of the transition and the focus on the communications and technical skills of the installers, whom they identify as vital ‘translators’ in the transition (thus reinforcing the idea of the importance of interconnections, and possible different types of stocks).

They also identify the planning, overall systems visualisation and research that went into the process prior to the switch, including on the uncertainties and the need for technical changes to existing appliances—because burners required higher airflow rates than town gas. This included the role of ‘Watson House’—the Gas Council’s national research centre—in field trials, development and approval of technology and communication of technical installation details. As such they argue that Watson House was fulfilling the role of a ‘translation hub’ which:

This notion of translation hubs or indeed individuals, aligns closely with ideas visible in the transdisciplinary research literature. Both refer to individuals or groups who cross knowledge boundaries, including across technical and social knowledge boundaries. The ‘translation hubs’ concept emphasises the importance of co-ordination activities across different domains and actors and is arguably a form of systems approach. This recognises the importance of dynamic behaviour between elements in the ‘actor network’ or system, since the coordination happens over time, and by definition is responsive to changes around it as well as changes in the technical installation details which affect the uptake of the new appliances.

Hanmer and Abram relate how the switch to natural gas also facilitated a much faster shift to central heating, aided by fixed price ‘packs’ including boilers, radiators and installation, with performance guarantees and with prices standardised on house size, which reduced uncertainty in the minds of households and provided easier pitches for salespeople. The change thus provided households with tangible benefits. This in a sense recognised the role of (positive) feedback loops in the system, since the fixed price pack reduced friction to installation, and likely made it simpler for salespeople to reach more people quickly, especially if the experience of the quick installation supported positive word-of-mouth feedback effects.

Similarly, they highlight how the natural gas transition and its dependent rise in gas central heating for the majority of UK homes has created a high level of ‘path dependency’. Homes are effectively locked into existing systems of natural gas boilers with wet radiators, which have become the default choice and create deep structural challenges for any future changes. This links to the next contemporary case we explore below, but in a negative feedback, slowing down the potential for change on account of the path dependency on a fixed type of technology and social systems around it.

While coming from different perspectives, both the analyses highlight the importance of planning, collaboration and communication across different stakeholders and perspectives, which is underpinned by a holistic understanding of the system. In particular they show the importance of an integration between technological solutions and policies, as illustrated by ensuring that conversion kits were created for multiple existing appliances and offered free of charge. The planners of the transition programmes thought through all aspects of the transition such as technical standardisation, costs concerns, orchestrated public information campaigns, emphasis on customer service, installer skills development, and so forth; to remove barriers and maintain progress. While the analyses by non-engineers were not framed in those terms they still highlighted the importance of transdisciplinary collaboration.

The exploration of this historic case supports two conclusions. The first is the importance of transdisciplinarity and (plausibly) transdisciplinary engineering in particular, given the emphasis on technical research on devices and installation approaches, as well as taking care of how people interacted and received these, and the governance of the system as a whole. The second is the relevance and validity of a systems approach. Both identified elements that aligned—some more obviously than others—with the key elements of a systems approach as set out by Arnold and Wade (2015). This strongly supports our hypothesis—alongside the other evidence concerning the rise of systems approaches in the UK government—that systems approaches have a general value in these areas.

At the same time, we recognise that a ‘systems approach’ is not the only useful perspective. For example, it could be seen as design problem, where the processes were designed to meet the needs of different stakeholders and foresaw multiple failure modes. However, the successful transition predates the development of design approaches such as design thinking (e.g., Brown, 2008). This transition problem has characteristics of wicked problems in the sense of Rittel and Webber (1973). Rittel, who was an urban planner, argued that ‘nearly all public policy issues’ (1973, p. 160), are wicked problems, that are ‘ill-defined’ and ‘malignant’. They cannot be ‘solved’ but require ‘elusive political judgement for resolution…over and over again’ (p. 160). However, unlike other wicked problems, in the case of town gas transition, the goal and the end state were clear, even though the details of the implementation required a multitude of flexible judgements.

This fostered a debate on the difference between scientific problems with clear descriptions and unambiguous solutions and complex social issues that need to be addressed by urban planners (see Crowley and Head, 2017). Later researchers drew the important distinction between problems that are wicked by nature and those that are wicked by design, while other argue that all design problems are a priory wicked (e.g., Coyne, 2005). These debates are beyond the scope of this paper, but the interplay of scientific ways and policy ways of thinking permeate into issues of engineering policy design. We suggest design approaches may also merit further consideration in these settings, but we leave that for other scholars or a future paper.

Having provided some validation to our hypothesis that transdisciplinary systems approaches naturally appear in other analyses we will now explore whether they can plausibly add value or insight to a current challenge.

Mains gas has been the fuel of choice in most dwellings since the 1980s. These systems principally operate via the national gas grid, supplying gas to an in-home boiler which burns the gas to heat mains water on demand. This water then circulates through pipework and radiators, providing space heating to the home. The majority of these units also provide domestic hot water either on-demand (a ‘combi boiler’) or via a separate hot water tank in a small number of older systems.

The formal starting point at which the UK government began to take action to incentivise homes to move from fossil-fuels to low carbon heating can be placed with the introduction of the Domestic Renewable Heat Incentive (RHI) in April 2014. This was an operating subsidy over 7 years for specific low carbon heating technologies such as biomass boilers, solar water heating and some heat pumps (Department of Energy Security and Net Zero, 2023). This means that the UK is already over 10 years into the transition. This is therefore a much slower and more gradual transition than the orchestrated shift from town to natural gas discussed in the previous case study.

Comparing UK census data on central heating fuels from the 2011 and 2019/2021 census indicates that the RHI did not lead to a substantial step-change in LCH uptake during the period (Figure 1). Gas heating decreased by 2.7% (if tanked or bottled gas is included in 2021 figures) and oil by 0.6%. Electric heating did not change, while two or more heating types, which is likely to include renewables such as solar thermal heating, increased by 4%, suggesting a small but only limited amount of progress.

Government policy shifted in 2021 with the publication of their Heat and Buildings Strategy (Department for Business, Energy and Industrial Strategy (BEIS), 2021), which emphasised the importance of heat pumps and particularly air-to-water heat pumps as a key transition technology for the majority of UK homes. In 2022, the RHI was closed and replaced in England and Wales with the Boiler Upgrade Scheme (BUS)—with a similar scheme in Scotland. This shifted subsidies to installation costs rather operational incentives and prioritised air-to-water and ground-to-water source heat pumps with a current grant of £7,500 towards their installation cost, with lower grants of £5,000 available for biomass boilers (UK Government, 2024).

The advisory Climate Change Committee (CCC) model a ‘balanced pathway scenario’ of decarbonisation, with mass deployment of air-to-water heat pumps in the UK’s 7th Carbon Budget (Climate Change Committee, 2025) and calculate that an annual installation rate of 1.5 million heat pumps per year by 2035 is required. In response to similar modelling in previous carbon budgets the Government set a target of 600,000 heat pump installations per year by 2028 (Department for Business, Energy and Industrial Strategy (BEIS), 2021).

This focus on air-to-water heat pumps and price subsidy interventions without any mandatory phase-out reflects a commitment in UK Government policy analysis to prioritise techno-economic efficiency as the driving priority. This is also visible in the CCC’s analysis (2025) and in academic and NGO policy analysis in this area (e.g., Hannon, 2015; Kokoni and Leach, 2021; Lowes et al., 2022). Fundamentally, it is fair to say that the UK approach to decarbonising home heating is dominated by one particular disciplinary perspective—that of economics. This is evident in the focus on financial subsidies for installations and installer training and regulatory changes around planning, recently announced. In a direct sense, this contrasts quite strongly with the systemic and transdisciplinary approach characterised earlier for the successful town gas case. We turn now to see how the difference in approach is affecting policy success.

So how is the UK performing in comparison to other European countries and against its own targets? From international investigations, the most recent comparable data covers up to 2021 in terms of heat pump installations as a percentage of population. The UK’s progress lags well behind that of 11 other Northern European countries—with a range of similar and different policy and technical contexts—for which data was available (Figure 2). Note that countries in southern Europe have been excluded from the analysis as they have a much higher proportion of air-to-air heat pumps, which are often used for both cooling and heating and which are very rarely used in the UK. The CCC also notes in the latest carbon budget that UK heat pump uptake is lagging behind comparable European Countries (Climate Change Committee, 2025).

National UK data from the Microgeneration Certification Scheme (MCS), the body that ensures installation standards and therefore eligibility for government support (e.g., RHI, BUS), shows that since 2009 255,316 air source heat pumps have been installed across the UK. The monthly and yearly installation numbers for air source heat pumps are shown for 2019 until the end of March 2025 (Figure 3). This is an average of 17,000 heat pumps a year over 15 years although with a slow but steady increase to around 55,000 heat pumps in 2024. This can be compared with the average 1.3million switches per year in the previous gas transition and is well below current targets. So why is uptake so low?

In a sense, the final part of the previous subsection hinted at the diagnosis for why the UK’s policy on domestic heat decarbonisation appears to be at best stalling if not outright failing. The clear focus on a mainly economic approach—perhaps underpinned by a technical one (focused on a certain sub-class of heat pumps technology)—is implicated here, in contrast with the successful transition to town gas explored earlier. We now look in more detail at the signs of a lack of transdisciplinarity in the area of UK domestic heat decarbonisation and with it a lack of supporting systems approaches.

A transdisciplinary systems approach emphasises the fundamental role of non-linearity, ‘feedback loops’, and the identification of different ‘levers’ to influence the system. The potential of this approach is illustrated by Figure 4, which shows a causal loop diagram (CLD). The elements of this CLD are coded into the three disciplinary areas used to sub-classify academic and non-academic research in this area. This illustrates how the different viewpoints can begin to be integrated. The point here is to illustrate how transdisciplinarity and systems approaches can manifest practically, in a way that is implementable in a policy setting. Of course, more detailed work is needed in validating first, the nature of the elements of this diagram—they are broadly in line with the elements identified in Tables 2, 3 but also contain insights from the authors, such as ‘technical complexity’. The use of CLDs also forces the user to think in terms of directionality as well as the nature of relationships between elements. This applies a discipline to the approach but is potentially constraining in an artificial sense, which is where a broader awareness of different methods—such as rich pictures—can be beneficial (Checkland and Poulter, 2020).

The CLD in Figure 4 has two reinforcing loops—key features of causal loop diagrams that help explain outcomes of system behaviour:

What both these reinforcing loops have in common is, on the one hand a relationship with the technical complexity of the technology, and on the other, an interaction of factors that cuts across social, economic and technical domains. A focus on the technical complexity of heating systems might give rise to wider strategies of decarbonisation in the UK that rely less on one specific type of heat pump and more on a wider array of technologies. This could include air-to-air heat pumps, various forms of heat and energy storage, local generation, district heating and direct electric where useful. The capacity for a nation to generate a wider array of diverse technical approaches can be understood as part of the engineering policy of a nation. This is something that has recently been raised as an important blind spot in policy communities (Cooper et al., 2023) and is generally overlooked in debates because air-to-water heat pumps have been identified as the most economically efficient heating decarbonisation strategy for the majority of UK homes (Climate Change Committee, 2025). However, this does not mean that it is the only or best option in all cases.

Looking at the technology ecosystem is also important for a transdisciplinary systems approach and by examining the lifecycle of a heat pump a different perspective on the process and its systemic interactions can be gained (see Figure 5). Current policy focusses on the installation stage of heat pumps and neglects the other lifecycle stages such as in-situ performance, interaction with other building systems, maintenance and user experience. However heat pumps and other low carbon heating systems can only make substantial contributions to carbon reduction if they perform effectively in the buildings in which they are installed and if they are well maintained. The lifecycle diagram therefore highlights a need for an increased focus on in-use performance through monitoring and guarantees, more engagement with households in using new systems and better awareness of maintenance needs and their effect on other parts of the system. This in turn could reduce the cost of ownership for homeowners.

Lifecycle approaches more broadly can also help identify key intervention points such as the importance of manufacturers, which are often overlooked in policy. They also show how causal loop diagrams (such as in Figure 4) might fit into or touch upon different systems across its life cycle, for example the effectiveness of heat pumps is greatly improved by other decarbonisation methods, which could also be insentivised by policy. This approach can allow decisions makers to navigate—and potentially organise pathways through—complexity in a system, without reducing it in ways that lead to suboptimal policy outcomes, such as the UK is currently experiencing—thus allowing them, in the framework of systems approaches set out above, to ‘retain but navigate complexity’.

While these two systems examples are only illustrative in nature—not expressly rooted in specific empiric research—the potential of adopting a systems approach in each of these areas is immediately apparent. As emphasised earlier, part of the insight from the systems approach proposed here rests on the transdisciplinary nature. Systems approaches and methods naturally allow for transdisciplinarity, but equally they can be applied in non-transdisciplinary ways (National Engineering Policy Centre, 2020) and doing so will limit the quality and range of insights.

We summarise our analysis by showing how key principles, introduced in section 2.3, of integrating transdisciplinary with a system approach could apply in the context of low carbon heating. These principles can help policy makers to predict the behaviour of the systems they are engaging in and thus recruit the relevant expertise.