Household carbon emissions from energy use are rapidly increasing in conjunction with growing urbanization; their reduction is critical for local urban climate improvement and the sustainable development of cities. Low-carbon behavior is proved as a key element determining residents’ lifestyle. Understanding how that behavior affects household energy use will be useful in promoting low-carbon households. In this study, Xiamen, a coastal city was divided into areas at high and low risk of flooding. We used the path analysis method integrated with behavior and socioeconomic factors to explore the mechanisms of low carbon behavior effects on household direct energy use and related carbon emissions. We found that socioeconomic conditions combined with low-carbon behavior had direct and indirect impacts on household carbon emissions. Low-carbon behavior in the high-risk area contributed most to reducing carbon emissions. Education level was the important factors in the low-risk area. Government-led policies encouraging low-carbon behavior were effective in reducing household carbon emissions in the high-risk area. However, in low-risk areas, education about a low-carbon lifestyle is an effective means for reducing carbon emissions.