M1703.3 "One opening shall be within 12 inches of the top of the enclosure and one within 12 inches of the bottom of the enclosure".

Now compare with IFGC 304 uses the phrase " commencing within 12 inches of the ....." Notice it did not say "reside entirely" or similar language. Compare this to the sections on emergency ingress and egress where it gives a reference point-- the sill height 44" above the floor. If it was that critical, they would have been more specific but this is intended to be an approximation. The air does not carry a ruler or go/ no-go gauge with it: Nope, I ain't going in there, the measurements aren't to spec. Air doesn't belong to the unions yet.

Guys, I think you're trying to pick fly poop out of black pepper here. If the opening starts within 12 inches of the floor or ceiling, it's cool. If it's within 14 inches, I'm not bitching. If its 2 feet away, I'd probably call it out. You gotta be reasonable here. The 12 inch thing has to do with not only room pressures but the natural convection patterns usually seen in heated homes.

If you stand in the middle of the room and rotate your arms in big circles like a helicopter, apply this motion to air flows. As room air hits the cool outer walls, it becomes denser so it falls to the floor. Warm room air rises up, hits the ceiling then mushrooms out to the walls, down, cools and completes this cycle. Smoke does the same thing during a fire. That's why the instructions tell you to place smoke and CO alarms about 18" from ceilings and walls. This phenomenon is known as the "cold corner effect". Very little air travels tight into the corners. Therefore, if you want to join in the room air, you have to have your entrance and exit ramps far enough away from the corners so traffic can flow smoothly, so to speak.

HTH

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disgusted with some people on this forum. Out of here!