Thanks for all the input. Some background info: The company doing the HVAC is not an HVAC firm but a company that specializes in outfitting portable/temporary shelters (tents, offices, controlled storage containers. We are doing the assembly and finishing of the offices. The offices in question range from 40 sqft to 360 sqft. Many of these offices are setup as "in field" workshops and often need ventilation for the activities (soldering, grinding, welding, gluing...). This is why the user has damper control. It has been considered to have an independent system for this ventilation but space, weight and power are all limited. I have found a reference in the Canadian building code that calls for 10L/second/person but I do not know the number of occupants in most cases. I was hoping there was a minimum based on sqft. I guess I will use a conservative max ocupancy and have them put a limiter on the damper to ensure there is sufficient fresh air for worst case. Thanks again, Chris