Combustion Air Vent terminating at Roof Top

[Clay White]

.............

[Bob Harper]

If you are talking about a woodburning fireplace, the inlet for a combustion air kit cannot be located higher than the point where it enters the Fp. One exception to this is where a mfr. allows for a vertical application in their listed instructions such as Heatilator. They allow the intake within 3 feet of the termination vertically as long as you form a trap at the base. Since this is a listed application, your AHJ should not fail this type of installation.

The hazard is that if the inlet is located in a negative pressure zone such as the lee of a house, it can actually draw flames out the air intake. Dale has a video of this happening.

HTH,
Bob