R1006.4

Section R1006.4 is titled 'Passageway' and covers requirements for providing combustion air into fireplaces. The minimum and maximum cross-sectional area for a combustion air duct, or where listed, to follow the manufacturer's installation instructions is established. The purpose of this section is to prevent carbon monoxide poisoning, oxygen depletion, explosions, and the building from catching fire.

The model shows 2 short sections of round combustion air ducts. The smaller duct has the minimum cross-sectional area allowed by this section and the larger duct has the maximum.