We see this application a lot: One roof with two different types of exhaust vents; ridge vents and roof louvers, for example. It's understandable why one would think that adding a different a second type of exhaust vent to the roof would improve the overall ventilation system. But that is not the case. Here's why it's a potential problem. The four main categories of exhaust ventilation products (ridge vents, power vents, roof/gable louvers, and wind turbines) function on different principles. If you mix or combine two or more of them on the same roof, short-circuiting could occur which could lead to weather infiltration and unbalanced airflow along the underside of the deck.

Let's say there's a ridge vent and some roof louvers on the same roof plus intake vents at the soffit. Although the ridge vents is supposed to pull it's intake air from the soffit vents, air follows the path of least resistance. The path of least resistance on this roof is the path between the ridge vent and the roof louvers. Therefore, the ridge vent can pull air from the roof louvers. As a result, portions of the lower part of the roof (below the roof louvers) are not being ventilated. Of worse consequence is the potential for the roof louvers to pull in weather.

In general, we recommend that you never mix or combine two different types of exhaust vents on the same roof. To avoid the short-circuiting problems, either remove the secondary exhaust vent from the roof or at least block off its opening so that it is not functioning.