The　selection　of　heat　radiator　has　a　non-negligible　impact　on　the　heating　effect　of　the　building.　The　rationality　of　the　radiator　selection　will　directly　affect　the　project　cost　and　actual　heating　effect.　Building　load　calculation　is　an　important　part　of　radiator　selection.　The　goal　of　this　paper　is　to　investigate　the　effect　of　internal　load　on　the　selection　of　radiator.　Taking　the　terminal　heat　radiator　in　one　dormitory　room　in　Beijing　as　the　example,　the　simulation　was　performed　using　DeST-h　software　based　on　the　actual　outdoor　meteorological　parameters.　Room　heat　loads　considering　the　room’s　internal　load　disturbances　and　not　considering　the　room’s　internal　load　were　calculated　separately,　by　which　the　radiators　were　selected,　respectively.　The　designed　supply-return　water　temperature　is　75/50 °C.　Then　DeST-h　software　was　introduced　to　simulate　the　heating　effect　of　the　room.　It　was　found　that　the　room　temperature　after　heating　in　consideration　of　room’s　load　disturbances　can　meet　the　comfort　requirements,　and　the　indoor　temperature　without　considering　the　internal　load　disturbances　in　the　room　may　be　excessively　high.　For　the　rooms　located　in　the　north　and　south　directions,　the　radiator’s　area　can　be　saved　by　18.9　and　20.3%　when　considering　the　room’s　internal　loads.　The　significance　of　this　research　is　that　it　has　an　important　role　in　the　correct　selection　of　the　radiator,　which　can　save　the　project　cost,　reduce　the　heating　energy　consumption,　and　provide　a　comfortable　indoor　thermal　environment.　©　2020,　Springer　Nature　Singapore　Pte　Ltd.