using any hid lighting i would recommend getting a good inline fan, being a 400 watt i would use atleast a 4" fan maybe a 6" depending on temps. good fans are fantech, vortex, can fan, ect. i would also recommend trying to exhaust the light to a complete other room than your grow box is in. you will be circulating the hotter air with the cool air

the best thing about using quality inline fans is you can also hook up aircooled hoods and carbon filters to the same fan(knockout most security and ventilation problems with 1 major purchase)