Answer: the air is forced into the mouths with a double flow VMC, which has two motors and is more expensive.
We differentiate between single flow VMC and double flow VMC, with their air intake. In a single flow system, air enters the housing naturally through grilles most often placed above the windows. While in a double flow system, the air is forced into the interior by vents installed in the living rooms, via a motorized mechanism. In both systems, stale air is then extracted using a motor in damp rooms (kitchen or bathroom). We therefore speak of single-flow VMC when only the extraction vents are connected to a motor, and double-flow VMC when the insufflation vents are also connected to a (second) engine. One motor for single flow, two motors for double flow. The price of the double flow CMV is therefore much higher than that of the single flow. You too, send us your brico question