I live on a small remote island and I'm building a cabin out of what once was a barn. My soffits are plywood with a 2.25" diameter hole in the center of each 16" OC roof truss. This has equated to a total of 26 holes on each side of the roof, as seen in the photo below. Since I made these soffits I don't have a NFA value given to me for each hole. I'm then having a difficult time balancing my exhaust venting since I'll be purchasing something to use for the exhaust. Since products are given with NFA values, such as roof static vents at 50" sq inch NFA, it doesn't seem to line up with simply calculating the area of all the circles for my intake.
In the picture below you can see I did that math, 52 holes with each hole being 10" area, that would equate to 520" square inches of open intake. But I do have rat wire and insect screen over the holes so they aren't pure unobstructed openings. I'm looking at static roof vents that have a 9"x9" square opening, wondering if I can do 9x9 = 81 square inches and be using that as a comparative value to my intake holes to find a balance.
The cabin is really quite small, as you can see, I kinda felt like 3 of these https://www.homedepot.ca/product/gaf-master-flow-50-sq-in-nfa-aluminum-square-top-roof-static-vent-in-black/1000405504# would be enough? But I don't want to have too much exhaust.... I'm stuck :( please help!