In this study, the possibilities to decrease energy consumption are analyzed in a thermally non-insulated old house in Belgrade, Serbia. By using EnergyPlus software, the space heating inside the old and refurbished houses is simulated for the single and combined refurbishment measures. The retrofitted houses are the house with thermal insulation of the external wall (H-IW), house with thermal insulation of the ceiling (H-IC), and house with lowering of the ceiling (H-LC). The houses with the combined refurbishment measures are house with the lowering of the ceiling and the modified thermal insulation of ceiling (H-ILC), and house with the lowering of the ceiling, modified thermal insulation of ceiling, and thermal insulation of the external wall (H-ILC&IW). The obtained results were analyzed for energy savings, investment, and investment return. It is found that the best single refurbishment measure has H-IW. The H-ILC gives the higher energy saving than that expected by the rule of thumb. The H-ILC&IW gives the lower energy saving than that expected by the rule of thumb. (C) 2012 Elsevier B.V. All rights reserved.