David,
IRC 2003 m1702.2 Confined Space. Where the space in which the appliance is located does not meet the criterion specified in Section M1702.1 two permanent opening going to adjacent spaces shall be provided so that the combined volume of all spaces meets the criterion. One opening shall be within 12 inches (35mm) of the bottom space, as illustrated in figure M1702.2. Each opening shall have a free area equal to a minimum of 1 square inch per 1,000 Btu/h(2201 mm 2/kw) input rating of all appliances installed within the space,but not less than 100 square inches (64415mm2)


Figure M1702.2 shows openings at the top & bottom.

If the appliances are direct-vent does not apply. M1701.1

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It Might have Choked Artie But it ain't gone'a choke Stymie!
Billy J. Stephens HI Service
Memphis TN.