Can anyone clearly explain where and how fresh air can make it into my mendota d40 gas insert hearth without mixing with the exhaust. On top of the colinear vent converter box are two separate ports, one that exhausts and one port that takes in fresh air. However on the bottom of the converter is only one outlet. What am I missing? Is it simple physics where the upward hot draft forces the exhaust out and the colder air has to come in and does not allow the hot exhaust that other exit option??