Venting systems shall be designed and constructed so as to develop a ______ flow adequate to convey all combustion products to the outside atmosphere.

The design and construction of venting systems are critical for ensuring safe and efficient removal of combustion products from heating appliances to the outside atmosphere. A positive flow in a venting system refers to a condition where the pressure inside the vent is greater than the atmospheric pressure outside. This positive pressure aids in effectively pushing the combustion gases out, reducing the risk of backdrafts and ensuring that all harmful gases, such as carbon monoxide and other by-products of combustion, are efficiently expelled.

Ensuring that the venting system develops a positive flow is essential for proper operation of the heating appliance. It promotes better airflow, which not only contributes to the efficient functioning of the appliance but also enhances safety by minimizing the potential for flue gas leakage into the living space.

Other flow types, such as negative or neutral, do not adequately maintain the needed pressure differential to ensure that all combustion products are efficiently expelled. Negative flow, in particular, can lead to backdrafting, where harmful gases flow back into the building, and neutral flow may not provide the necessary momentum needed to transport exhaust effectively. Therefore, a venting system designed to develop a positive flow is vital for both the performance of the HVAC system and the safety of the building's occupants.