Building pressurization calculations has long been one of the unknowns to most HVAC professionals. We have always wondered how much air we need to pressure a building. NFPA and ASHRAE have publications which define this based on building type, number of doors/windows, construction type, etc. We have created a simple spread sheet which makes it easy to accomplish this task. This goes together with door closure forces calculations. Some buildings in toxic chemical industry environments have to be pressurized to higher pressure to prevent infiltration of toxic gases during blasts. Door closure forces has to be adjusted to account for this. There are several other considerations especially w.r.t. ceiling, door undercut, pressurization air distribution, etc. Contact me for further information and details.