for a 400 watt cooltube you want a minimum of about 465cfm to properly cool the bulb. i'm not sure watt 465cfm converts to in metric, sorry. i had a 400hps cooltube with only 4inch duct booster and it wasn't so good but i upgraded to a 465 squirrellcage fan going by specs on the cooltube package and it was 100x better. with the 465cfm 400hps cooltube i could keep the temps in the closet the same as the ambient temp in my house at all times!
justaseed Reviewed by justaseed on . Ventilation Duct Fan For COOLTUBE Question I'm hoping to use it to make a cooltube for a 400w HPS, alternatively a 250HPS. Will this do? These are the specs: TD 160/100. 2 speed: 2500/2100 v/min. Effect 35/23 W. Decibel 39/35 dB(A). Max. air: 160 m³/tim. Rating: 5