I have to rough in appliance vents on a house so drywall may be installed. Using Centrotherm Innoflue S636 single wall for the appliance vent. The appliance will be direct vent. Will be using Innoflue for the fresh air as well, this product has directional flow arrows. Would like the option of using either of the two roughed in pipes as the exhaust, so naturally I would need to ensure that the flow arrows are both pointing to the outdoors. My question is, can anyone see an issue with combustion air piping installed "opposite to flow"?