Building information modeling (BIM) is considered as a major trend of the construction industry in the future. In traditional way for estimating the cost of the HVAC system in buildings, a lump sum method is adopted as a rough approximation. Instead of detailed quantity calculation, the lump sum method often result in inaccurate total cost and quantities. The purposes of this study is to promote the BIM to the owners and MEP designers. This research found that the BIM software needs to be updated and revised. By building detailed HVAC system components of a completed public office building, the overestimation of HVAC budgets has been revealed in the case study. The contractor has earned an extra profit about 3.9% of the total project cost due to the overestimated quantity of HVAC components in the building.