A sustainability assessment, i. e. life-cycle assessment, is conducted to reduce the environmental impacts of all stages of a product``s life cycle, from production to disposal. This life-cycle assessment is a technique used for the scientific and quantitative measurement of pollutant emissions and resource consumption. During the assessment, a list of inputs and outputs is compiled and analyzed, their environmental impacts are assessed, and the results are interpreted to serve the study purposes, helping develop an environmentally friendly product design and an improvement strategy. In this study, two types of portable fan heater use (A and B) were evaluated for energy efficiency and environmental friendliness. The analysis results revealed that the heating panel and motor parts had high environmental impacts and were therefore selected as environmental improvement targets, and the improvement strategy was developed to divide the airflow rate into high, medium, and low, just like ordinary fans. Using this technique, the study found that the heating panel and motor parts had poor energy efficiency. Once the strategy was implemented through the life-cycle assessment, their energy efficiency improved dramatically.