A study on ventilation design using the spreadsheet model is carried out to propose means of available design. A sample of complex ventilation system in the non-standard condition is used to illustrate this spreadsheet model. In developing the spreadsheet model, this study has attempted to it general by using computional equations and design parameters that can be readily applied to any spreadsheet software. Also, most design data is contained in the spreadsheet template. This template provides the same design information as the ACGIH worksheet, and operates quickly and efficiently, and is flexible enough to use under different conditions. spreadsheet model allows the ventilation engineer to design quickly and accurately the ventilation system, without spending too much effort in the design process. By storing on computer and diskette, the design data computed finally can be used as a permanent record of specific ventilation system, and because of flexibility to be able to design over and over again while making only slight changes to the input data, the spreadsheet model is used availably to accomplish the design optimazation by redesign and troubleshooting by review from field measurements. Also, the spreadsheet model is available for designing ventilation system under different condition or evaluating existing system or design drawing, because changes in the layout or formulae can be readily made to fit the needs of the designer.