Background: I am planning to wall off my mechanical area which will create a confined space, according to code definitions of < 50cu.ft. / 1kBtuh. Free advice from a HVAC pro acquaintance suggested putting grills on the new wall. However, I would have to vent two walls to make up the required space. If I am reading the code guide (not full code definitions) correctly, that would be four vents total since each wall needs two-one in the upper 12" and one in the bottom 12". On the new wall I would need to filter it since my woodworking shop is on the other side which produces saw dust and fine particles that probably are not ideal for combustion air. Question: I'd like to bring in the combustion air from outside. Code guide says a single opening is allowed. The ceiling of my basement is just above grade (> the 12" above grade req.) Can I get away with one pipe in the upper 12" of the mechanical room? By my math, it would take a 7" pipe to make up the required CA. Or, do I have to have two. If so, how would I get away with having one in the bottom of the room and one in the top. I have attached a layout of the room. Dimensions of the "fun room" are estimates. https://picasaweb.google.com/lh/photo/Hly7e6Hst1Rg_RlptPM9LKKHuuq2nkCP0ygbl-VB1bM?feat=directlink Thanks so much for reading. I really appreciate it.