Review of the Role of Heat Pumps in Decarbonization of the Building Sector

Abstract

The transition to low-carbon heating systems is fundamental to achieving climate neutrality, particularly within the building sector, which accounts for a significant share of global greenhouse gas emissions. Among various technologies, heat pumps have emerged as a leading solution due to their high energy efficiency and potential to significantly reduce CO₂ emissions, especially when powered by renewable electricity. This systematic review synthesizes findings from the recent literature, including peer-reviewed studies and industry reports, to evaluate the technical performance, environmental impact, and deployment potential of air source, ground source, and water source heat pumps. This review also investigates life cycle greenhouse gas emissions, the influence of geographical energy mix diversity, and the integration of heat pumps within hybrid and district heating systems. Results indicate that hybrid HP systems achieve the lowest specific GHG emissions (0.108 kgCO₂eq/kWh of heat delivered on average), followed by WSHPs (0.018 to 0.216 kgCO₂eq/kWh), GSHPs (0.050–0.211 kgCO₂eq/kWh), and ASHPs (0.083–0.216 kgCO₂eq/kWh). HP systems show a potential GHG emission reduction of up to 90%, depending on the kind of technology and energy mix. Despite higher investment costs, the lower environmental footprint of GSHPs and WSHPs makes them attractive options for decarbonizing the building sector due to better performance resulting from more stable thermal input and higher SCOP. The integration of heat pumps with thermal storage, renewable energy, and smart control technologies further enhances their efficiency and climate benefits, regardless of the challenges facing their market potential. This review concludes that heat pumps, particularly in hybrid configurations, are a cornerstone technology for sustainable building heat supply and energy transition.

1. Introduction

Many countries in the world declared to be carbon neutral by 2050. One of the areas, where decarbonization looks very promising, is connected with the heat supply system in buildings. As of now, heating systems globally still account for a significant share of carbon dioxide emissions—37% of global CO₂ emissions [1].

However, there are many new technologies that help to reduce the carbon footprint of heating in residential, commercial, and industrial buildings. They include the following: the adoption of heat pumps, district heating networks, power-to-heat solutions, and energy storage technologies. These solutions vary in efficiency, cost, and feasibility depending on geographic, climatic, and economic factors [2].

District heating (DH) systems represent one of critical approaches to decarbonizing building heat supply. Traditionally reliant on fossil fuels, modern district heating networks are increasingly integrating renewable energy sources, waste heat recovery, and energy storage. Dong et al. (2025) [3] explored the optimized design of hybrid energy systems for building clusters, emphasizing the importance of integrating wind power, solar energy, and thermal storage within district heating networks. Their study found that coupling these elements can lead to a 30–50% reduction in carbon emissions compared to conventional gas-based district heating. Moreover, low-temperature district heating (LTDH) has emerged as an effective solution to improve system efficiency. Unlike conventional high-temperature district heating, LTDH operates at lower supply temperatures (50–70 °C), reducing heat losses and enabling the integration of industrial waste heat, geothermal energy, and heat pump technology. Lu et al. (2024) [4] examined the role of thermal energy storage (TES) in low-temperature district heating systems, finding that building-integrated TES can store excess heat from renewable sources and discharge it during peak demand periods, enhancing overall system flexibility.

Another promising approach to decarbonizing heating is power-to-heat (P2H) technology, which involves converting surplus renewable electricity into thermal energy. Xu et al., 2025 [5] analyzed the dual-objective optimization of solar-driven power-to-heat systems, concluding that battery storage combined with thermal storage significantly improves energy self-sufficiency in solar-rich areas. This aligns with findings by Bacci et al. [6], who demonstrated that multi-energy systems (MES)—which integrate electricity, heating, cooling, and transportation—are crucial for achieving deep decarbonization in urban districts.

Furthermore, hydrogen-based heating has been explored as a complementary solution to electrification. Deshko et al. (2024) [7] examined the role of hydrogen boilers in low-carbon building regeneration, highlighting that hydrogen can be a viable alternative in areas with existing gas infrastructure. However, the study also noted that green hydrogen production remains costly, requiring further advancements in electrolysis and energy storage technologies.

Beyond technological advancements, the integration of smart energy management systems is proving to be a crucial factor in optimizing decarbonization strategies. Artificial intelligence (AI) and machine learning algorithms are increasingly being utilized to predict heating demand, optimize heat distribution, and improve overall system efficiency [8]. AI-driven systems can analyze real-time weather data, building occupancy, and historical energy consumption patterns to dynamically adjust heating supply, thereby reducing energy waste and improving system responsiveness.

The adoption of digital twin technology in urban heating networks has also gained traction. Digital twins allow for real-time monitoring and simulation of energy flows within a heating system, enabling operators to make data-driven decisions regarding energy dispatch and storage. Kimanya et al. (2025) [9] explored the use of digital twins in airport energy infrastructure, finding that integrating machine learning with real-time heating system modeling led to a 15% improvement in energy efficiency. Similar results were observed by Hirano et al. (2025) [10], who demonstrated that AI-enhanced local energy planning in decarbonized communities can optimize heat pump scheduling and district heating dispatch.

Another innovative approach involves thermal energy storage (TES) combined with AI-based forecasting. Hoffmann, 2025 [11] examined the impact of predictive energy management in vertical greenery systems, where building-integrated green facades not only act as passive insulators but also help regulate indoor temperatures, reducing heating demand in winter and cooling demand in summer. The study found that coupling vertical greenery systems with AI-driven thermal storage optimization resulted in a 20% reduction in peak heating loads, offering a cost-effective supplement to active heating technologies.

While heat supply decarbonization is a central focus, reducing overall heating demand through deep energy retrofits is equally critical. Reina et al. (2025) [12] highlighted the importance of improving building insulation, enhancing air tightness, and utilizing high-performance windows in reducing heating loads. Their research demonstrated that comprehensive energy retrofits can cut heating demand by up to 60%, making it significantly easier to transition to low-carbon heating solutions.

An emerging field within deep retrofitting involves prefabricated facade systems with active thermal components. Monteleone et al. (2024) [13] investigated hygrothermal performance of prefabricated facades, showing that integrating heat recovery ventilation (HRV) and solar-assisted thermal panels within prefabricated facades can enhance indoor comfort while minimizing heating demand. Such solutions are particularly effective in historic buildings where traditional insulation measures may be difficult to implement.

One of the most widely recognized technologies for decarbonizing heat supply is the heat pump. Heat pumps use electricity to extract thermal energy from air, ground, or water, significantly improving energy efficiency compared to conventional fossil fuel-based heating systems. When powered by renewable electricity, heat pumps can achieve near-zero operational emissions. A study by Namdar et al. (2025) [14] highlights the integration of heat pumps with solar photovoltaics (PV) as a promising solution, particularly in positive energy districts where buildings generate more energy than they consume. Their research found that a well-designed heat pump and PV system can cover nearly 90% of heating demand in buildings while significantly reducing reliance on the grid.

Despite their advantages, heat pumps face several challenges, including performance degradation in cold climates and high upfront investment costs. To mitigate these issues, hybrid heat pump systems have been proposed, combining heat pumps with supplementary heating sources such as district heating or hydrogen boilers. Xue (2024) [15] investigated the role of hybrid ground-source heat pumps in educational buildings, demonstrating that coupling heat pumps with low-temperature district heating networks can enhance system resilience and reduce peak electricity demand. Their findings suggest that optimizing the control strategies of heat pumps in district heating networks can further improve overall efficiency and reduce carbon emissions.

Within the EU, heat pumps are acknowledged as a key renewable energy technology in legislative frameworks, playing a crucial role in the European energy and climate strategies for 2030 and 2050. The EU’s heat roadmap for 2050 envisions a great integration of heat pumps in both individual and large-scale applications, predominantly leveraging waste heat and renewable resources [16].

The aim of this review is to assess the role of heat pump technology in the decarbonization of building sector. The growing popularity of heat pumps and the emerging operational problems caused are often the subject of discussions regarding their actual impact on the environment and related emissions. The purpose of taking up the topic is the need to answer the question about their actual potential for reducing CO₂ emissions compared to other commercially available heat sources and technologies listed above, taking into account a number of technical and operational conditions as well as the global diversity of the energy market.

2. Methodology of Review

An electronic search was performed using the Scopus and Web of Science databases, selected for their rigorous scientific standards and extensive scope. To initiate the research, we developed key terms and employed a systematic, phased approach to filter out articles that did not align with our criteria. We focused on specific parameters, such as publication date and document type, to refine our search. Only research articles published in English were included in this review. We meticulously screened the titles and abstracts for relevance, excluding works that were not appropriate, as presented in Figure 1.

After removing duplicates and inaccessible articles, we conducted thorough full-text readings to verify the credibility of the selected studies, assessing their design, methodology, and relevant outcomes. The literature review was based mainly on Scopus and Web of Science databases, with additional search conducted in Google Scholar and IEEE Explore. Industry and scientific reports were also used, including the following: ACEEE Report, Aalto University Energy Reports, LUT University Energy Reports, Iris Unipa and Joint Research Center. The keywords were “heat pump”, “heat pump in building sector”, “heat pump & decarbonisation”, “heat pump efficiency”, “heat pump LCA”, and “ASHP/GSHP/WSHP carbon dioxide emissions”. The timespan of the analysis is presented in Figure 2. 50% of the reviewed articles is no older than the last two years and 90% being no older that the last five years.

The inclusion criteria were as follows: (i) peer-reviewed journal articles or authoritative institutional reports, (ii) studies published in English, (iii) focus on heat pump technologies in the context of building sector decarbonization, (iv) availability of full text for critical appraisal, and (v) publication date not older than six years (with exceptions made for foundational or particularly relevant earlier works, such as key technical reports).

Exclusion criteria comprised: (i) conference abstracts without full papers, (ii) studies lacking methodological transparency or quantitative data, and (iii) publications not directly related to the environmental or technical assessment of heat pump systems. The selection process involved title and abstract screening, followed by full-text review, with studies retained based on their methodological quality, relevance to this review’s aims, and clarity of reported outcomes.

3. Assessment of Heat Pumps Potential in Decarbonization

This section is divided into six subsections in order to provide a precise description of the main aspects influencing the decarbonization potential of heat pumps, so that technical aspects (Section 3.1), environmental impact (Section 3.2), the impact of global diversity of the energy market on electric heat pump emissions (Section 3.3), integration of heat pumps in hybrid systems (Section 3.4), synergetic effects of technology, economy and environment (Section 3.5) as well as advantages and disadvantages of heat pumps together with market barriers and incentives (Section 3.6).

3.1. Technical Aspects of Heat Pumps’ Utilization

The transition to sustainable heating solutions is a crucial aspect of global decarbonization efforts, particularly in the building sector, where heating accounts for a significant share of energy consumption and greenhouse gas emissions. Heat pumps have emerged as a primary technology for reducing carbon emissions while maintaining energy efficiency [17]. By transferring thermal energy from the air, ground, or water sources, heat pumps offer a highly efficient alternative to conventional heating methods that rely on fossil fuels.

Heat pumps’ operation rule is based on the process of transformation of free or waste energy into higher-temperature heat through a closed-loop process. Operating on a reversed Carnot cycle, they harness low-temperature heat, elevate it to a higher temperature, and distribute it throughout a building. Various types of heat pumps are available on the market, differentiated by their operational principles, heat sources, applications, or scales. Typically, heat pumps are categorized based on their heat sources (Figure 3) as follows [18]:

• Air source heat pumps (ASHPs) utilizing ambient air as their heat source, delivering heat either directly through air (air-to-air) or via hydraulic systems (air-to-water).
• Ground source heat pumps (GSHPs) extracting heat from the ground; utilizing geothermal energy through ground heat exchangers or borehole heat exchangers.
• Water source heat pumps (WSHPs) extracting heat from water, employing local water resources such as wells, streams, lakes, and ponds through either open- or closed-loop systems.

The most important technical factors connected with utilization of heat pumps are presented in

Table 1. Selected technical aspects of heat pump performance recognized in the literature.

Aspect	Air Source Heat Pumps (ASHPs)	Ground Source Heat Pumps (GSHPs)	Water Source Heat Pumps (WSHPs)	Source
Temperature Stability	Variable—heavily influenced by weather conditions	Highly stable—underground temperatures remain constant	Highly stable—groundwater Moderately stable—surface water	[19]
COP range in heating mode	~2.0–4.5	~3.5–6.5	~3–6	[20,21,22,23,24,25] 1
Sensitivity to Ambient Conditions	High	Low	Low to moderate, depending on the kind of water used	[23,24]
Installation Cost	Generally lower; preferred in mild climates	Typically higher due to ground loop installation (drilling/excavation)	Generally higher or similar to GSHPs, with specific site conditions affecting cost	[18]
Supply temperature [°C]	up to 65	up to 70	up to 70 2	[26,27,28]
Operating temperature range [°C]	−20 to +35	−10 to +25	+5 to +25	[26,27,28]
Sound level [dB(A)]	<68	<55	<55 2	[26,27,28]
Investment cost [€/kW]	>700	>1100	>1800	[29]

¹ This study also includes comparative data for water-to-water configurations. ² Adopted from GSHP catalogs due to the similarity of units.

.

The quantitative comparison of technical parameters in Table 1 reveals distinct operational characteristics among heat pump types. Ground source (GSHP) and water source (WSHP) heat pumps typically offer higher supply temperature limits (up to 70 °C), allowing compatibility with conventional radiator systems, while air source units (ASHP) generally reach up to 65 °C. The technical aspects affecting the performance of heat pumps can be discussed on the basis of temperature stability connected with the type of heat source. In these terms, ASHPs operate under a wide range of outdoor air conditions (−20 to +35 °C), which can significantly affect seasonal performance. In contrast, GSHPs and WSHPs benefit from more stable underground or water source temperatures, ranging from −10 to +25 °C and +5 to +25 °C, respectively.

These thermal advantages contribute to improved seasonal performance. As shown in the SCOP values, GSHPs achieve the highest seasonal efficiency (up to 5.0), followed by WSHPs (up to 4.5), and ASHPs (typically between 2.8 and 3.5). These differences confirm that systems with more stable and moderate source temperatures (GSHP, WSHP) tend to achieve better year-round energy efficiency and are more suitable for colder climates or high-temperature heating demands.

Since ground (or groundwater) temperatures remain relatively stable and warmer than winter air, GSHPs can operate with COPs that are nearly constant throughout the season, so their sensitivity to ambient conditions remain low. This is expressed in the results of the case study in Perth, Australia, comparing open-loop GSHP vs. ASHP in identical houses. The results showed that the GSHP’s average heating COP was ~3.9, essentially unaffected by outdoor temperature, whereas the ASHP’s heating COP varied from 1.9 to 2.9 depending on ambient conditions [30].

Air source heat pumps have lower and more variable seasonal heating efficiency because outdoor air temperatures fluctuate widely and drop in winter. In mild climates, modern ASHPs can still perform with the sufficient SCOP if well-designed. The Italian study by Rossi di Schio et al. (2021) [31] found that an ASHP in a mild coastal city (S. Benedetto) had an effective SCOP at around 2.86–2,99, whereas in a cold alpine climate (Livigno), the same ASHP’s SCOP dropped to about 2.72–2.83. Moreover, the defrost cycles needed to clear ice noticeably reduced the seasonal COP of ASHP. While SCOP was about 2.93 in the first location mentioned, it raised to 3.09 if defrosts were neglected—it presented a roughly 5% drop due to defrost energy needs.

Compressor heat pumps can vary in construction, which affects their efficiency. The type of refrigerant used, including its thermodynamic characteristics and environmental impact (e.g., GWP, pressure glide), is also important since it influences the thermodynamic cycle efficiency. Low-GWP refrigerants like R-290 or R-454B can provide better COP and a lower environmental impact, though their flammability or toxicity may require additional design considerations. Among others, CO₂ heat pumps (R744) have emerged as a promising alternative in domestic hot water (DHW) applications due to their low global warming potential (GWP = 1) and ability to deliver high-output temperatures above 60 °C. Recent developments have demonstrated their applicability in centralized DHW systems for multi-family buildings, using swing tank configurations to improve thermal efficiency and reduce cycling losses. Such systems achieve seasonal performance coefficients (SCOP) of around 3 under real-life operation, making them both environmentally and technically viable [32].

Generally, modern refrigerants have comparable or slightly improved performance. A performance comparison indicated that a heat pump using R32 (mildly flammable, low-GWP) can have about 9–10% higher COP and capacity than the same system with R410A [33]. Research by Xue (2025) [15] found that new refrigerants and variable-speed compressors significantly enhance the coefficient of performance (COP) of air source heat pumps, ensuring reliable operation even under sub-zero conditions. Essadik et al. (2024) [34] introduced a multi-valve flexible heat pump system with latent thermal energy storage, which significantly reduces defrosting energy losses and enhances overall system performance. This innovation is particularly beneficial for air source heat pumps, which experience efficiency degradation due to frost accumulation.

Moreover, the design and technology of evaporators and condensers (e.g., microchannel coils, enhanced surface treatments, and anti-frost coatings) can also bring about enhancement in heat transfer rates, reduce refrigerant charge, and minimize losses due to frost or fouling, thereby boosting overall efficiency of the heat pump [35].

More sophisticated compressor technology and cycle enhancements (variable-speed compressors, vapor injection, two-stage compression, and enhanced defrost controls) allow the heat pump to operate efficiently under varying load conditions and extreme temperatures, improving part-load performance and extending operational range. Heat pumps with inverter-driven, variable-speed compressors generally achieve higher SCOP than traditional on/off units. Variable speed allows the heat pump to modulate capacity and run more continuously at part load, avoiding inefficiencies from frequent stop–start cycles. In a direct comparison study, the inverter system showed at least ~10% higher SCOP than the on/off unit [36,37]. Smart control tools can also shift load to more favorable periods and reduce unnecessary energy consumption, leading to significant improvements in seasonal efficiency [38].

Beyond compressor-based technology, absorption heat pumps are gaining attention in scenarios where low-temperature heat sources are available, such as industrial waste heat or solar thermal collectors. These systems can achieve COPs between 1.8 and 2.0, depending on the working pair (e.g., water/LiBr or ammonia/water) and boundary conditions. Integrated into district heating or process cooling networks, they offer considerable potential for reducing primary energy demand and CO₂ emissions. Their economic feasibility has been demonstrated in several studies, with payback periods and investment returns improving under high fuel cost scenarios [39]. The required heating output temperature (to the indoor space or hydronic system) has a strong effect on SCOP. Lower-temperature heat distribution (e.g., radiant floor heating at 30–40 °C or fan coil units at ~45 °C) allows the heat pump to run at a higher COP than in the traditional range of supply water temperature 55–65 °C for radiators or domestic hot water [40].

The proper sizing and installation quality, including site-specific considerations (e.g., soil conditions for GSHPs, water availability for WSHPs) can also be treated as one of the key technical factors. Correct sizing and installation ensure the system operates at its design point. Poor installation can lead to significant energy losses, while optimized integration can enhance performance by matching the system to the specific demands of the residential building, as well as bring about visible improvement in environmental performance of the system [41].

Finally, the integration of the heat pump with other systems (e.g., domestic hot water, solar assistance, or waste heat recovery) into hybrid systems and integration with renewable sources like photovoltaic installations can shift operation to more efficient conditions and improve overall seasonal performance by reducing reliance on auxiliary heating. Furthermore, hybrid heat pump systems that integrate with district heating networks have been proposed as a transitional strategy for cities seeking to phase out fossil fuel heating while maintaining system resilience [4]. Recent studies have demonstrated that integrating solar photovoltaic (PV) systems with heat pumps further enhances efficiency and reduces dependence on the electrical grid. In particular, research by Essadik et al. (2024) [34] explored the performance of solar-powered heat pumps in different climate zones, showing that PV-assisted systems can provide up to 80% of a building’s heating demand when appropriately sized.

To sum this section up, it is necessary to underline that each of the factors mentioned above contributes to the overall efficiency and seasonal performance (SCOP) of heat pumps. Advances in each area—from refrigerant selection to sophisticated control strategies—are continuously driving improvements in residential heat pump technology. Investigating the seasonal coefficient of performance of heat pumps is vital, leading to the optimizations in design and operation, as well as the system performance and cost-effectiveness of heat pump installations.

3.2. Environmental LCA of Heat Pump Systems and GHG Emissions

Although heat pumps belong to commercially available and mature technologies used in decarbonization [42] and emerged as a promising alternative for residential heating systems, it is still essential to regularly evaluate their performance to ensure sustainability and reduce environmental impacts. This part of the review explores the current literature on environmental studies, mostly Life Cycle Assessments (LCAs) performed for domestic heat pumps in residential buildings, evaluating their environmental impacts at each stage of the life cycle, with special focus on GHG emissions and parameters used in these assessments.

The concept of Life Cycle Assessment (LCA) emerged during the 1960s due to concerns about environmental deterioration, particularly limited resource availability [43]. For many years, LCA has been utilized within the heat pump sector [44]. As an effective diagnostic tool for monitoring product performance, LCA has significantly contributed to enhancements in this technology over the years. Numerous comparative studies have assessed the environmental impact of HP systems in relation to traditional heating systems [45,46,47]. These LCA studies have employed various Life Cycle Impact Assessment (LCIA) methods to analyze the environmental effects, including CML2001 [47,48,49,50,51,52], IMPACT2002+ [53], ReCiPe [45,48,54,55,56,57], and the Environmental Footprint [58,59,60] methods. Despite their energy efficiency, HP systems can still lead to environmental repercussions, primarily due to greenhouse gas (GHG) emissions arising from refrigerants and the carbon dioxide emissions linked to the electricity required to operate them. The Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), and Ozone Depletion Potential emerged as the most commonly investigated impact factors [48,49,50,51,61].

Many findings indicated that replacing traditional heating systems—such as natural gas furnaces, oil or bio-oil boilers, biomass boilers, or coal boilers—with heat pump systems led to a reduction in these environmental impacts [48,49,50,61,62,63]. However, variations in functional units and system boundaries have resulted in a limited number of papers that could be directly used in comparison of emission level in this study, with a focus on decarbonization. The examples of such research are summed up in

Table 2. Comparison of greenhouse gas emissions from selected types of heat pumps.

General Type of HP	Decarbonization Potential	GHG Emission kg CO2 eq/kWh *	Reference
ASHP	70% lower carbon intensity compared to gas boiler	0.083 *	[55]
ASHP	-	0.216 *	[64]
ASHP Water Heater	GHG reductions compared to natural gas systems	0.19–0.21 *	[20]
ASHP	54% reduction	0.111	[65]
ASHP	54% average reduction in recent dwellings	-	[66]
GSHP	-	0.211 *	[64]
GSHP	Lower carbon emissions than ASHP	0.098 *	[61]
GSHP	Lower carbon emissions than ASHP	0.194	[67]
GSHP (Vertical/Horizontal/Helix heat exchangers)	HP with vertical heat exchangers shows the lowest GHG emissions	0.02–0.08	[41]
GSHP	Reduced emissions by 35.23%; sensitive to electricity mix	-	[54]
Wastewater Heat Pump	GHG emissions reduced by 3.6–4.1% due to heat pump integration in district heating	~0.01	[68]
WSHP	The water source heat pump causes the lowest GHG emissions in relation to ASHP and GSHP	0.213 *	[69]
WSHP (River water system with PV supply integrated with district heating)	Combined systems can significantly reduce greenhouse gas emissions across their life cycle compared to traditional heating and cooling systems	~0.112 *	[70]
WSHP	Significant potential of reduction; most of carbon dioxide emission is associated with operation and maintenance	0.018	[71]

* positions recalculated from total lifetime emission or from MJ, GJ, to kWh due to the lack of data.

, where studies on ASHP, GSHP, and WSHP greenhouse gas emissions are presented. It is necessary to underline that WSHPs are represented by a limited number of papers available for comparison within the assumed timespan of this study; therefore, this kind of heat pumps will be separately discussed at the end of this section.

It should be noted that the results presented in Table 2 are drawn from multiple studies with different methodological assumptions. These include variations in system boundaries, life cycle inventories, assumed operating conditions, and emission factors of local electricity mixes. While the table provides an overview of indicative GHG emission levels for ASHP, GSHP, and WSHP systems, direct quantitative comparisons should be interpreted with caution due to the underlying heterogeneity of the data sources. Only studies that applied life cycle assessment (LCA) methodology and reported quantitative results (or allowed for recalculation based on provided data) were selected. Moreover, the comparison focuses exclusively on stand-alone heat pump systems without integration of other renewable energy technologies (e.g., PV or solar thermal).

As presented in Table 2, all the examined systems are characterized by the decarbonization potential when compared to conventional ones. In some cases, the direct comparisons between the types of heat pumps were studied [41,55,62]. These examples clearly indicate a greater decarbonization potential when using ground source heat pumps (GSHPs) compared to air source heat pumps (ASHPs). This is because, as demonstrated in Section 3.1, the seasonal coefficient of performance (SCOP) for ground and water source heat pumps is higher, resulting in reduced energy consumption for operating the system. Most studies concluded that the usage phase together with production were the primary contributors to the overall environmental impact of heat pumps, overshadowing other stages like raw material extraction, device installation, and end-of-life disposal. Even the most efficient heat pumps utilizing renewable energy sources displayed notable environmental impacts, as reported by several researchers [48,49,50,51,61].

As presented in Figure 4, the maximal values of emissions found in the literature research present the lowest level in the case of WSHPs. However, as mentioned before, due to the lack of relevant studies, the examples taken for comparison also included solar-supplied and combined systems; therefore, their general emission level should be treated as comparable to GSHPs or slightly better, as reported in [69]. Despite the expenditures required for the installation of ground heat exchangers and the use of brine, ground source heat pumps exhibit a lower average level of carbon dioxide emissions compared to air source heat pumps. This indicates that the dominant factor influencing emissions is the system’s operational energy consumption from the grid, which outweighs the impact associated with equipment manufacturing and system construction. However, as presented in Figure 4, the minimal level of carbon dioxide emission related to ASHP can be, in some cases, lower than the mean emission calculated for GSHP and WSHP. This is connected with technical details of a unit, localization, the whole system design, and supply power environmental quality.

A recent comparative LCA study across climates in Europe found that GSHP systems had 8 to 43% lower environmental impacts than equivalent ASHP systems when providing heating to the same building. The advantage of GSHPs was most pronounced in cases with high heating demand (colder climates) in relation to their higher efficiency. The only exception noted was in Sweden, where the electricity was already almost entirely renewable/nuclear; there, the operational emissions of both heat pump types were so low that the extra materials for the GSHP slightly tilted the balance in favor of the simpler installation of ASHPs. Therefore, in an ultra-low-carbon grid, the incremental benefit of GSHP’s efficiency is negligible, and minimizing hardware (as with ASHP) can become environmentally preferable. However, in most regions (especially those with moderate grid carbon intensity), the GSHP’s reduced electricity use more than compensates for its higher upfront footprint, yielding net GHG savings relative to ASHPs [58].

As mentioned before, water source heat pumps have been recognized for their potential to reduce greenhouse gas emissions in residential heating applications in a limited number of papers, with functional units varying from those selected for comparison. The key findings can be presented on the basis of the most important publications in this area.

In [72], the CO₂ emissions of a conventional gas heating system can be reduced by 15% through the implementation of a water source heat pump (WSHP). Despite the WSHP relying on electricity—which has a higher carbon emission factor compared to gas in Korea—the HP system still achieves a reduction in CO₂ emissions. This is primarily due to a 46.2% decrease in energy consumption when using the WSHP.

In another study on WSHPs, the extent of carbon emission reduction varies notably depending on the type of water source utilized. Specifically, average reductions are observed as 11.1% for river water, 16.9% for raw water, 18.6% for underground water, and 15.4% for deep-sea water. These variations correspond closely with the changes observed in energy-saving rates. The heating efficiency increases with higher water temperatures and is further enhanced during prolonged heating periods. Consequently, the differences in energy consumption associated with various water sources result in substantial reductions in carbon emissions, yielding positive outcomes across all water types. Furthermore, carbon emission reductions were affected by the distance of water intake, showing a decrease of 1.2–6.5% per 100 m, both in horizontal and vertical directions [73].

To sum this section up, it is crucial to emphasize that the main factors affecting the emission level are connected with the type of heat source, its temperature range, and the whole system design affecting SCOP, as well as supply power environmental quality. Indirect emissions related to the operational phase of a heat pump life cycle are the essential elements of its environmental balance.

3.3. Geographical Differences in the Decarbonization Potential of Heat Pumps

Fluctuations in the electricity mix powering residential buildings can significantly influence environmental performance of heat pumps and their GHG emission [74]. By understanding the sources of electricity generation, one can comprehensively assess the environmental footprint associated with heat pump operations, anticipate energy costs, and shape policies aimed at enhancing sustainability and energy security. According to the IEA reports, currently used heat pumps with F-gas refrigerants, despite the possibility of leakages, still enable the reduction of greenhouse gas emissions by at least 20% compared to efficient gas boilers, even when using electricity with a large carbon footprint. Reductions of 80% or more have even been achieved in countries with cleaner energy mixes. These values can be improved by using alternative refrigerants. Such a large variability is mainly related to differences in the emission intensity of energy generation, not the choice of refrigerant [75].

The environmental performance of heat pump systems is strongly influenced by the carbon intensity of the electricity mix in a given region. To illustrate this dependency, a sensitivity analysis using national grid emission factors reported by the International Energy Agency (IEA, Paris, France) for selected European countries can be useful [76]. For example, the emission factor in Poland (approx. 700 gCO₂/kWh) is significantly higher than in France (approx. 60 gCO₂/kWh), which results in notably higher operational emissions for electricity-driven systems like heat pumps. Assuming an average SCOP of 3.5 for a GSHP, the resulting specific GHG emissions caused by grid dependency would vary from ~0.20 kgCO₂/kWh in Poland to ~0.017 kgCO₂/kWh in France. This shows that the carbon benefits of heat pumps are maximized in regions with cleaner grids, and highlights the importance of aligning decarbonization strategies in the building sector with ongoing efforts in power sector transformation. In the following paragraphs, the selected examples of heat pumps’ potential for decarbonization will be discussed on the basis of the literature review focused on the energy mix differences.

3.3.1. Canada

Canada has one of the cleanest electricity profiles among major nations—roughly 80% of Canadian electricity are from low-emission sources. Hydropower alone contributes about 60–62% and nuclear about 13%, leaving less than 20% from fossil fuels (mostly gas, with coal now under 7%) [77]. Canada’s energy market is highly diverse, with significant regional variation in the greenhouse gas intensity of electricity generation. Provinces like Quebec (4.46 gCO₂/kWh), British Columbia (22.58 gCO₂/kWh), and Prince Edward Island (20.34 gCO₂/kWh) demonstrate some of the lowest GHG intensities, reflecting a strong reliance on renewable sources such as hydroelectricity. In contrast, provinces and territories such as Nunavut (840.00 gCO₂/kWh), Nova Scotia (682.36 gCO₂/kWh), or Alberta (662.76 gCO₂/kWh) show the highest GHG intensities, indicating a greater dependence on fossil fuel-based electricity generation. This disparity highlights the uneven progress toward decarbonization across Canada’s regions [78]. However, in ultra-low grid carbon markets, heat pumps can achieve high GHG savings. Replacing a fuel boiler with a heat pump in Canada can reduce 70–80% of heating-related CO₂ emissions [75].

3.3.2. Europe

Europe’s power supply is increasingly low-carbon. Many European countries have decarbonized significantly, like France where its grid is dominated by low-carbon nuclear energy, whereas others (like Poland) still rely heavily on coal [75]. As a result, replacing gas boilers (dominant in EU) with heat pumps already yields major greenhouse gas reductions and is crucial for RePowerEU. Even in regions characterized by a carbon-intensive electricity grid, such as the Czech Republic and Greece, the deployment of air source heat pumps (ASHPs) in newly constructed residential buildings contributes to a net reduction in climate change impacts. In countries like France, Norway, and Sweden, the relative mitigation effect is approximately 90%, despite significant differences in heating demand. Specifically, heating requirements in Norway and Sweden are nearly three times higher than in France, with corresponding ASHP capacities being up to five times greater, primarily due to colder climatic conditions. Nonetheless, the significantly lower carbon intensity of electricity in Norway and Sweden offsets the decreased coefficient of performance (COP) associated with lower ambient temperatures, resulting in comparable climate benefits. For existing older buildings, ASHPs facilitate a reduction in climate impacts—measured using the GWP100 metric—in 15 out of 18 countries assessed. France, Norway, and Sweden continue to exhibit reductions at nearly 90%, consistent with findings in new buildings. However, in the context of older buildings in the Czech Republic, Greece, and Poland, the environmental benefits of ASHPs are not guaranteed. In these cases, while newer dwellings still show a decline in climate impacts, older building stock may experience an increase unless the national electricity mix undergoes significant decarbonization [66]. Notably, refrigerant leaks constitute a relatively minor share of lifecycle emissions in comparison to the CO₂ from electricity use, especially as grids become cleaner [58,79].

3.3.3. USA

In the U.S. electricity mix, about 20% of energy comes from renewables, resulting in emission factor of 400 gCO₂eq/kWh [76]. This yields a moderate carbon intensity for grid electricity. Even so, shifting from fuel-fired furnaces to heat pumps reduces emissions from the residential sector. A recent analysis covering 550,000 U.S. homes found that electrifying heating with air source heat pumps cuts lifetime GHG emissions in every U.S. state, even those with coal-dominated grids. In a very carbon-intensive grid, a heat pump still yields at least a ~20% GHG reduction versus an efficient gas boiler [80]. This is because heat pumps are 3–5× more efficient in converting energy to heat than combustion devices, so they require far less primary energy even if that electricity is generated from fossil fuels. Another study with population-weighted US average results showed emission reductions for a heat pump over a gas furnace to be 38–53% for carbon dioxide [81]. As the U.S. grid incorporates more renewables, the GHG advantage of heat pumps will correspondingly grow [80].

3.3.4. China

China’s electricity generation is still based mostly on fossil fuels (predominantly coal), with the remainder from renewables (mostly hydro) and a small nuclear share. Consequently, China’s grid carbon intensity (in the order of 550–600 gCO₂/kWh) is among the highest of these regions [75]. Despite this, using heat pumps for heating in China can substantially lower emissions compared to traditional coal or gas heating. The data analyzed in [82] contains three scenarios. In the current scenario, only 1% of medium–low temperature heat is replaced by HPs, resulting in annual carbon emissions of 2528 MtCO₂. Under the natural growth scenario, with HPs covering 20% of the heat demand and a higher COP of 2.50, emissions drop to 1554 MtCO₂. This represents a 38.5% reduction compared to the current scenario. In the significant growth scenario, with 60% HP adoption and the same COP, emissions further decrease to 945 MtCO₂, achieving a 62.6% reduction relative to the current scenario. These results highlight the substantial decarbonization potential of electric HP adoption in China’s heating sector, especially if coal furnaces are replaced. The decarbonization potential is significant and will intensify as China’s grid cleans up [82].

Summing up the geographical differentiation focused on energy mix, it is necessary to underline that even in carbon-intensive energy markets, electric heat pumps have the potential for decarbonization, especially in modern dwellings. As countries shift to cleaner energy sources, the carbon savings from heat pumps will increase. The cleaner the electricity, the more effective heat pumps will be, highlighting the connection between electric heating and renewable energy growth, as presented in Figure 5.

3.4. Hybrid Systems and Their Potential for Decarbonization

Heat pumps are flexible in operation and may be easily integrated within conventional or renewable energy sources, as well as innovative technologies of energy storage or district heating networks.

The integration of thermal energy storage (TES) with heat pumps has gained significant attention. TES systems store excess heat generated during periods of low demand and release it when needed, reducing strain on the electrical grid and enhancing the efficiency of renewable energy utilization [3]. Among various TES technologies, phase-change materials (PCMs) and water-based storage tanks have shown the highest potential for improving heat pump performance. Research by Essadik et al. (2024) [34] found that TES integration can reduce peak electricity demand by up to 40%, making heat pumps more adaptable to fluctuating renewable energy supply.

Another critical consideration in heat pump adoption is the role of hybrid heating systems, particularly in retrofitting older buildings. While heat pumps perform efficiently in well-insulated buildings, their performance in poorly insulated structures remains a challenge. Research by Bacci et al. (2025) [6] indicates that hybrid systems combining heat pumps with hydrogen boilers or backup electric heating can provide a feasible transition pathway, allowing buildings to benefit from low-carbon heating while addressing peak demand challenges.

District heating integration presents a particularly promising approach for regions with existing centralized heat supply infrastructure. Studies by Vivier et al. (2024) [83] have explored how heat pumps can supplement or replace fossil fuel-based district heating networks, particularly when combined with large-scale thermal energy storage. By using excess electricity from renewable sources, district heating networks powered by heat pumps can achieve greater flexibility and lower carbon emissions, offering a scalable solution for urban areas. Additionally, low-temperature district heating (LTDH) systems powered by heat pumps are emerging as a scalable solution for urban areas. Unlike traditional district heating networks, LTDH operates at lower temperatures (50–70 °C), significantly reducing heat losses and enabling the efficient integration of heat pumps, industrial waste heat, and geothermal energy [6]. Studies by Lu et al. (2025) [4] and Xue (2025) [15] confirm that LTDH networks equipped with heat pumps can reduce carbon emissions by up to 60% compared to gas-based district heating while maintaining cost-effectiveness.

Moreover, high-temperature district cooling is a possible area of HP usage. The evaluation of district system in Gothenburg, Sweden, indicated that the actual chilled water temperatures for the buildings ranged at 6–16 °C for supply and 8–25 °C for return when the outside temperature reached 25 °C or higher. It was found that the amount of free cooling nearly doubled when the supply and return temperatures in the district cooling system increased. The study identified challenges and opportunities for the current district cooling system, assuming that high-temperature district is a component of a future intelligent energy system, which incorporates significant amounts of renewable energy and offers cooling solutions for buildings that are more energy-efficient and have reduced cooling needs [84].

Another key technology for improving heat pump adoption is sector coupling, which involves integrating heating, cooling, and electricity systems to maximize energy efficiency and reduce overall emissions. In this approach, heat pumps are combined with renewable electricity generation, battery storage, and district heating networks to create a flexible and resilient energy ecosystem [2]. A study by Jansen et al. (2024) [85] explored the benefits of using excess electricity from wind and solar farms to power heat pumps, demonstrating that this approach not only stabilizes the electrical grid but also reduces dependency on fossil fuel-based backup heating.

Another important technology introduces a novel waste heat recovery system designed to reduce heating and cooling energy consumption in both data centers and residential areas through the implementation of a water source heat pump. Although carbon dioxide is emitted during processes such as pipe manufacturing and excavation, these emissions are classified as indirect and contribute less than 1% of the total CO₂ output, given that they occur only once during the system’s installation phase. The majority of emissions are indirect, primarily resulting from energy consumption. This highlights the importance of reducing CO₂ emissions associated with electricity generation. Accordingly, enhancing system performance by reducing energy demand is key to lowering carbon emissions. The examined system demonstrated a significant improvement, consuming 18.8% less energy than its conventional counterpart and achieving a 28.7% reduction in CO₂ emissions over a 15-year operational period [86].

A study on residential buildings in Ireland found that hybrid heat pumps can achieve primary energy savings of up to 73% and carbon footprint reductions of 44% compared to conventional systems [87]. In non-residential EU buildings, hybrid ground source heat pumps coupled with radiant emission systems can reduce annual median primary energy and CO₂ emissions by half, reaching 25 kWh/(m²·a) and 5 kgCO₂/(m²·a), respectively [88]. Air source heat pumps have an estimated global warming potential of 35.8 t CO₂ equivalent over a 17-year lifetime, with operational footprints varying significantly based on country-specific electricity carbon intensities [89]. The carbon footprint of heat pumps can be further reduced by using renewable energy sources like photovoltaic solar energy for electricity supply.

More examples of hybrid HP systems are presented in

Table 3. Carbon dioxide emission reduction potential and emission levels.

Type of Hybrid HP System	Functional Unit/Case Description	CO2 Emission Reduction Potential	Emission kg CO2 eq/kWh	Reference
Dual-Source HP Various energy mix	1 MJ of energy	Reduced carbon emissions compared to conventional systems	0.101–0.318	[64]
Photovoltaic-driven Reversible HP	1 kWh thermal energy	Significant emission reductions due to renewable energy integration	0.072	[52]
Multi-source ASHP Operation with renewable energy sources	1 m2 of heated area during 15 years of operation	Zero operational CO2 emissions possible with renewable integration	0	[90]
Dual-source Solar-Assisted HP	Yearly operation	GHG reductions of 50–80% can be achieved	-	[91]
ASHP + Renewable Natural Gas	1 MJ; operation in selected years	Reduction compared to conventional sources	0.019–0.157 *	[92]
Hybrid GSHP	20 years of operation	Reduced emissions by optimizing energy source usage	-	[93]
Advanced control strategies for hybrid GSHP	1 year of operation	3000 hybrid heating systems providing heat for 100,000 dwellings would have avoided 38,000 tons of CO2eq	-	[94]
Waste HP combined with district heating	1 MWh of heat produced	GHG emission reduction by 42%	0.175	[95]

* positions recalculated from total lifetime emission or from MJ, GJ to kWh due to the lack of data.

, discussing carbon emission reduction potential as well as emission levels related to particular cases. The mean emission in Table 3 accounts approximately 0.108 kg CO₂eq/kWh for HP hybrid systems, excluding the studies with a lack of data and various functional units. This could be compared with the previously studied data in Figure 3, where the mean emissions calculated for grid-supplied ASHPs and GSHPs were slightly higher. This allows renewable energy supplying the HP system, as well as its integration with other systems, to contribute to the reduction in CO₂ emissions and enhance the potential for decarbonization, as mentioned in the literature.

Integration with renewable energy sources, such as solar photovoltaic and wind energy, enhances the sustainability of heat pump systems. When coupled with smart grid technology, heat pumps can adjust their operation based on real-time electricity availability, ensuring that heating demand is met using low-carbon electricity sources [96].

Research has shown that heat pump systems combined with PV panels can cover up to 80% of a building’s heating demand, reducing dependency on external energy sources [97]. Moreover, studies by Saleem et al. (2024) [98] and Dong et al. (2025) [3] have demonstrated that combining heat pumps with phase-change materials (PCMs) for thermal energy storage can enhance performance during peak demand periods, mitigating fluctuations in electricity supply and demand.

3.5. Synergetic Effects of Technology, Economy, and Environment Through International Case Studies

While previous sections discussed technical and environmental aspects of heat pump systems separately, their real-world performance and feasibility are determined by the interplay between economy and the mentioned two domains. In practice, a system with slightly higher investment costs may offer superior seasonal efficiency and significantly lower emissions, leading to long-term economic and environmental advantages. To capture this multi-dimensional perspective, the following section explores the synergetic interplay between technology, economy, and environmental outcomes using selected international case studies. Each example demonstrates how the synergy between technical, economic, and environmental performance shapes the overall assessment of system viability. This integrative approach allows for a more nuanced understanding of which technologies are most appropriate under given boundary conditions.

A case study from Germany, including a recent techno-economic model by Roth et al. (2024) [99] evaluated national target of reaching 10 million heat pumps by 2030. The study explored multiple integration scenarios involving heat storage, PV systems, and demand-side management. The results indicated that combining heat pumps with decentralized thermal storage and solar PV could reduce the country’s gas demand by 25% and halve building sector CO₂ emissions. The economic rationale was also strong: the hybrid system reduced the need for costly grid-scale battery investments and allowed consumers to benefit from dynamic electricity tariffs.

A case study from Alaska focused on resilience and low-temperature performance of heat pumps. In remote Alaskan communities, diesel-based heating has traditionally dominated, resulting in high emissions and fuel costs. However, a pilot project in the city of Sitka installed advanced cold-climate ASHPs capable of operating at temperatures down to −25 °C (Sustainable SouthEast Partnership, 2022) [100]. The result was a 65% reduction in annual heating costs and an 80% drop in CO₂ emissions when powered by a local hydroelectric grid. Although the capital costs were subsidized by state-level energy funds, the long-term savings proved the model economically replicable in other Arctic or sub-Arctic regions.

A case study from the Netherlands offers a compelling example of system-wide transition, from gas to all-electric power supply. As part of the “Natural Gas-Free Neighbourhoods ” program, over 100 pilot communities have transitioned to all-electric heating or district heating systems [101]. Many rely on hybrid HP systems combining gas boilers for peak demand and HPs for baseline loads. A techno-economic assessment by the Dutch Environmental Agency showed that such hybrid systems can reduce CO₂ emissions by up to 70% with minimal retrofit costs. However, their success depends on grid stability, consumer behavior, and sustained political commitment.

A study by Wang et al. [102] examines a hybrid system consisting of an air source heat pump (ASHP) directly coupled with a photovoltaic/thermal (PV/T) collector and supported by both thermal energy storage. The system was designed for domestic hot water production in a residential setting under variable solar and load conditions. Integration of the PV/T unit improved the seasonal performance by stabilizing the heat pump’s electricity input, reducing reliance on grid electricity during peak hours. Life cycle analysis indicated significant GHG emission reductions compared to stand-alone ASHP systems, although the exact CO₂ values were not provided. The system achieved annual electricity savings of approximately 23% (based on SCOP), with an estimated payback period over 10 years, demonstrating long-term economic viability. This example highlights the synergistic interaction between technological optimization (hybrid integration), environmental benefit (lower emissions), and economic return (energy cost savings), confirming the added value of integrated system design in low-carbon building applications.

3.6. Advantages and Disadvantages of Heat Pump Technology

Despite their significant advantages, heat pumps face technical and economic barriers, including high initial investment costs, performance limitations in extreme cold climates, and the need for retrofitting in existing buildings [4]. Addressing these challenges has been a focus of recent research, leading to the development of hybrid systems that combine heat pumps with thermal energy storage, district heating, and alternative heating sources, as well as energy performance improvements.

One of the most prominent advantages of heat pumps is their high energy efficiency. Unlike traditional heating systems, which generate heat through fuel combustion, heat pumps utilize electricity to move heat from one place to another, achieving a coefficient of performance exceeding 3.0 in many applications [103,104]. This means that for every unit of electricity consumed, heat pumps can provide three or more units of heating energy, leading to significant reductions in primary energy use and carbon emissions when powered by renewable electricity [98]. The efficiency of heat pumps has been particularly well documented in moderate and warm climates, where they can operate year-round with minimal performance degradation.

Another key advantage of heat pumps is their versatility in providing both heating and cooling. In addition to space heating, many heat pumps can reverse their operation to provide cooling during the summer months, making them a year-round climate control solution [105]. This dual functionality makes them particularly attractive for residential and commercial applications in regions with variable seasonal temperatures.

However, heat pumps also present certain disadvantages and challenges, particularly in cold climates, retrofitting applications, and cost considerations.

One of the main drawbacks is the performance degradation of air-source heat pumps in extremely low temperatures. Since air-source heat pumps extract heat from ambient air, their efficiency decreases as outdoor temperatures drop, resulting in higher electricity consumption and increased reliance on backup heating systems [106]. In contrast, ground source and water source heat pumps maintain more stable performance in colder climates but require higher installation costs and extensive land or water access for implementation [17].

Additionally, the high upfront cost of heat pumps compared to conventional heating systems remains a significant barrier to widespread adoption. While operating costs are generally lower over the long term, the initial capital investment for heat pumps—including equipment, installation, and potential building modifications—can be two to three times higher than that of gas boilers [96,103]. Government incentives, rebates, and financing mechanisms have been introduced in many countries to offset these costs, but adoption rates still depend on financial feasibility and consumer awareness [97]. Several policy mechanisms have been implemented to address financial barriers, including grants, tax rebates, low-interest loans, and carbon pricing schemes [17]. Research by Carnieletto et al. (2024) [96] shows that subsidies covering 30–50% of heat pump installation costs can significantly increase adoption rates, particularly in the residential sector. Additionally, energy performance standards and regulatory mandates—such as bans on new fossil fuel boiler installations—are helping drive market transformation.

To optimize lifetime expenses, some studies have proposed the use of hybrid ground source heat pump systems, which combine the lower upfront costs of conventional solutions with the reduced operational expenses characteristic of GSHP technologies [107,108]. Nevertheless, while this approach may offer economic benefits over the system’s lifespan, it is not necessarily aligned with environmental optimization. Due to their high efficiency, GSHP systems are generally associated with lower greenhouse gas emissions than conventional heating and cooling technologies.

Recent studies underline that the economic viability of heat pump systems strongly depends on contextual factors such as scale, financing conditions, and local electricity tariffs. A particularly valuable example is presented by Stanytsina et al. [109], who conducted a comparative analysis of levelized cost of heat (LCOH) for both implemented and calculated HP systems in Ukraine. Their findings demonstrate that the actual investment costs for GSHP systems typically range between 800 and 1500 €/kW, with the heat pump unit representing only 20–40% of the total capital cost. In contrast, for ASHP systems, the unit often constitutes 60–65% of the total investment, especially in small-scale installations. Moreover, the authors highlight how LCOH is highly sensitive to SCOP values and financing scenarios. For instance, an increase in the discount rate from 0% to 10% leads to a doubling of the LCOH in several GSHP cases. Their analysis also confirms that electricity tariff structures—particularly time-of-use pricing—can enhance or limit the competitiveness of HP systems compared to centralized heating.

Another challenge associated with heat pumps is the need for building insulation and efficiency improvements to maximize their effectiveness. Older buildings with poor insulation and leaky envelopes may not fully benefit from heat pumps unless extensive energy retrofitting is undertaken. Research by Zhou et al. (2024) [105] highlights that in poorly insulated buildings, heat pumps may struggle to maintain consistent indoor temperatures, leading to higher energy consumption and reduced cost-effectiveness. Retrofitting measures, such as better insulation, triple-glazed windows, and air sealing, are often necessary to optimize heat pump performance, which can add to the overall project costs [103,104].

Additionally, the complexity of installation and maintenance is often cited as a disadvantage of heat pump systems. While gas boilers and electric resistance heaters are relatively simple to install and operate, heat pumps require specialized design considerations, proper system sizing, and regular maintenance to ensure optimal efficiency [98]. In particular, ground source heat pumps require subsurface drilling, which may not be feasible in densely populated urban areas due to space constraints and installation costs [96].

In some cases, grid capacity limitations and peak electricity demand issues also pose challenges to large-scale heat pump deployment. The electrification of heating through heat pumps increases overall electricity demand, potentially straining power grids, particularly in regions with limited renewable energy capacity or aging grid infrastructure [17]. To mitigate these challenges, thermal energy storage and demand-side management strategies have been proposed, allowing heat pumps to store excess heat during off-peak hours and reduce strain on the grid during peak demand periods [106].

Another key aspect of heat pump deployment is grid integration and infrastructure upgrades. Since electrification of heating increases overall electricity demand, governments and utilities must invest in grid modernization, renewable energy expansion, and demand response programs to accommodate widespread heat pumps [106]. Demand-side management strategies, such as time-of-use electricity pricing and dynamic load balancing, can further optimize heat pump operation and reduce pressure on the grid [105].

In addition to technological advancements, policy and financial incentives play a crucial role in accelerating heat pump adoption [110,111]. Studies by Lu et al. (2024) [4] and Jansen et al. (2024) [85] highlight the impact of government subsidies, tax incentives, and carbon pricing mechanisms in encouraging homeowners and businesses to switch to heat pump technology. Their findings suggest that well-designed financial incentives can shorten the payback period for heat pump investments, increasing adoption rates and facilitating the phasing out of fossil fuel heating systems.

4. Conclusions

This review confirms that heat pumps represent a mature and versatile technology with substantial potential to decarbonize the building heating sector. Key conclusions can be summed up in following points:

• Comparing the performance of HPs, ground source and water source heat pumps typically offer higher seasonal performance and lower greenhouse gas emissions than air source systems, particularly in regions with moderate or carbon-intensive electricity grids. GHG emissions per unit of heat delivered, as analyzed in the literature, are as follows: WSHPs (0.018 to 0.216 kgCO₂eq/kWh), GSHPs (0.050–0.211 kgCO₂eq/kWh), and ASHPs (0.083–0.216 kgCO₂eq/kWh).
• Life Cycle Assessments reveal that operational emissions, driven largely by electricity consumption, dominate the environmental footprint of heat pumps. Therefore, the decarbonization of the electricity grid directly enhances the sustainability of heat pump systems.
• The climate impact of heat pumps varies significantly across regions due to differences in heating demand and energy mix. Even in high-carbon intensity regions, heat pumps outperform fossil-based systems, and their benefits grow as the grid becomes greener. In low-carbon energy grids, reduction of emissions reaches 90% when compared to gas boilers.
• Hybrid systems combining heat pumps with district heating, thermal energy storage, or renewable energy can further reduce emissions and improve performance, making them a strong candidate for retrofits and high-demand scenarios. The analyzed literature examples of hybrid heat pump systems report an average specific GHG emission of 0.108 kgCO₂eq per kWh of heat delivered.
• Despite their advantages, widespread adoption of heat pumps faces technical and economic barriers such as high upfront costs, retrofitting challenges in older buildings, and grid capacity limitations. Policy support through subsidies, performance standards, and infrastructure investments is essential to accelerate adoption.

In conclusion, heat pumps are a key element of building sector decarbonization. Their integration with other sustainable technologies and supportive policy frameworks will be critical for achieving climate goals and fostering energy-efficient, low-emission heating systems worldwide.