The development of microorganisms that colonise heating, ventilation and air conditioning (HVAC) system give the arisen of ‘sick building syndrome’ and ‘building related illness’ which have potential to adversely impact human health such as infections, allergy and toxic effects. A dirty HVAC system cannot provide adequate heat transfer and will reducing efficiency of the system, at the same time it can reduce the equipment life and failure of expectancy. In this paper, the contamination present by dirt and microorganisms on HVAC system can be reduced by cleaning and eliminates the bio film with multi-enzyme based product. The expertise in the field clearly shows that those organisms captured from the environment are more robust and opportunistic than those which have been bred in laboratories for many generations. For this reason, in field trial studies, micro-organisms from actual sites; HVAC system at Penapisan PETRONAS buildings located in Kerteh, Malaysia were used. Data of air flow, temperature and microorganisms were taken before and after treatment were done. Results show that energy conservation effect saved through the treatment is up to 13%.