The purpose of ventilation is to maintain temps and humidity in the centre of the plant canopy. Generally, it is preferable to have too much ventilation than not enough. Replenishing the air in the room provides more co2 for your plants.
Glandore Hydro stocks a wide range of high quality inline fans for hydroponic growing indoors. Inline fans are compact, low profile and speed controllable. Available in a range of sizes.