Is there a rule of thumb for room pressurization? Assuming a "tight" room, how much outside air do I need to bring in to hold a positive pressure, say 0.5" WG for example. Is there a simple formula based on room volume or square footage?
There is no thumb rule, per se, depending upon floor area or room volume and also there are no leak tight rooms practically. Referring the thread given below gives you an idea of how to do the calculation.