How high must a mechanical draft venting system terminate above any forced-air located within 10 feet?

A mechanical draft venting system must terminate at least 3 feet above any forced-air inlet located within 10 feet to ensure that exhaust gases do not re-enter the building through the air intake. This height helps to create a safe and effective separation between the exhaust and fresh air intake, preventing any potential backdraft or contamination of the airflow that could occur if the gases were allowed to enter through the forced-air system. Adequately spacing the vent termination helps maintain the performance of both the venting and the forced-air system, ensuring safety and efficiency in the operation of heating appliances.