## 4 Factors Affecting HErC
### Energy Consumption Features  
China's energy transition has played a significant role in carbon reduction. This transition involves not only the cleaning of energy sources but also the optimization of energy usage behaviors and the improvement of household energy intensity and efficiency. These three aspects, energy sources, energy end-use, and energy usage processes, collectively influence HErC [55].  
Energy sources and structure are critical factors affecting urban HErC. Extensive household surveys indicate that, despite notable urban-rural and north-south disparities in China, the energy consumption structures for key activities such as cooking and space heating have been significantly optimized [27]. Particularly, the \"coal-to-electricity\" initiative has significantly reduced HErC by electriying activities like transportation, heating, and cooking [56]. The shift from coal to natural gas in kitchens is also a major factor in carbon reduction [42]. However, studies also highlight regional inequities in the transformation of energy structures [57]. In some areas, changes in the primary energy structures for electricity and heating are minimal [48], resulting in less effective emission reductions following the energy transition [34]. This highlights that cleaning energy sources is key to reducing carbon emissions. To achieve greater reductions, both cleaner energy sources and energy structure transformation must progress together.  
As a significant determinant of household energy end-use, energy use behavior is a major factor driving inequities in HErC. Research indicates that these patterns are closely related to household type [27], largely due to differences in traditional culture and climate adaptation among households [58]. In addition, household energy use behavior marked seasonal variations. [PERSON] et al. segmented urban household energy consumption in Chinese provinces into five end uses and demonstrated through inter-provincial comparisons that climatic, economic, and cultural differences significantly influence household energy use behavior [6]. [PERSON] et al. quantitatively demonstrated that behavioral adjustments can reduce household cooling electricity consumption by 35% while maintaining current service levels [59]. [PERSON] et al. argued that actual demand and economic status drive differences in household energy consumption behaviors by influencing psychological motivations [60]. Correspondingly, enhancing residents' awareness of climate change and energy conservation can prompt them to adopt voluntary energy-saving practices, thereby optimizing household energy use [24].  
Enhancing household energy intensity and efficiency, meaning reducing carbon emissions per unit of energy consumed, is central to household carbon reduction strategies [47]. [PERSON] et al. found that reductions in energy intensity contributed to up to 89% of the decrease in urban residential carbon emission intensity [61]. Energy efficiency gains can be achieved through both technological innovations and behavioral changes [24; 62; 63]. However, the rebound effect may limit these emission reductions [64]. [PERSON] et al. noted that the actual reduction achieved through enhanced household energy intensity and efficiency often falls short of expectations because cost savings are redirected toward activities that lead to additional energy consumption and emissions [65]. Moreover, the effectiveness of energy intensity reductions varies across regions and time. Reductions in energy intensity have been shown to mitigate residential carbon emissions in eastern regions [66], while in other areas, such reductions may even promote carbon emissions in some years [67]. Although enhancing household energy intensity and efficiency plays a key role in reducing carbon emissions, its full potential remains constrained by factors such as the rebound effect.