The objective of this study is to find the differences between EnergyPlus and Korean web-based energy performance assessment tool by comparing heating load. A practical apartment house was modeled in EnergyPlus and web-based tool, and simulated changing the various conditions such as building area, balcony, air exchange rate, u-value, window area, and building direction. The basic model, south directed apartment house without balcony, showed 30.9% of relative difference between E+ and web-based tool. The heating load in E+ was significantly influenced by solar heat gain because the result of no window model showed good agreement with E+ and web-based tool. Also heating load change rate of two tools showed similarity when u-value conditions were changed. And with respect to balcony and window-wall ratio condition, two tools showed different results. When the air exchange rate were changed, heating load of E+ were more sensitive than web-based tool.