Household energy-saving behaviour reduces greenhouse gas emissions, which is crucial for combating climate change and contributes to multiple sustainable development goals (SDGs), particularly SDG7 (Affordable and clean energy), SDG12 (Responsible consumption and production), and SDG13 (Climate action). This study investigates how two types of environmental knowledge and two categories of environmental concerns influence consumers’ attitudes towards energy saving, leading to their curtailment behaviour and purchases of energy-efficient appliances. The study also examines the spillover effect from curtailment to purchase behaviour. Survey data collected from 405 Vietnamese consumers were analysed through partial least squares structural equation modelling. The results reveal the role of specific knowledge about energy conservation and concern about energy shortages in promoting energy-saving attitudes. The findings also confirm a positive impact of EEA purchasing behaviour on curtailment behaviour. This study advances the knowledge-attitude-behaviour theory by validating a model that simultaneously examines different types of environmental knowledge and concern. It is among the first to demonstrate a spillover effect between two energy-saving behaviours. This study’s fresh insights offer implications for researchers and practitioners developing education and communication strategies to promote energy conservation.