stuck on ventilation

I am converting a metal storage cabinet ( 3w x 2d x 6H ) into stealth box. I now have lighting (remote digital ballast, 400W HPS & MH ),and Cool Tube. This will be located in an uninsulated garage in south USA=heat. I am resigned to to the fact that my season will be limited to six or seven months at best.

I`m thinking passive ventilation system. I prefer to use 4" outlet & inlet holes reason being six inch holes are harder and more costly to drill.I am not opposed to using a six inch fan if need be.

Two questions; If growing only 3 or 5 plants will I need air filter (must be stealth)? Can I attach fan to light>filter>exhaust or fan>light> exhaust.than filter?

Also what size CFM fan and matching sized filter ( it`s kind of cramped in there once cool tube is hanging)?

Thanks in advance,You people have great info that you share.

I didn`t think it was that hard of a question.

You'll only be able to grow well when you're below around 85f ambient temp, maybe a little higher, but you know that.

400w puts out pretty good heat, I'd say you should be looking at 6" ducting even though you don't want to do it. 6" also makes stealth possible as a 4" would have to make a lot of noise to cool 400w but a 6" can be throttled back to running more silent.

Yes you can use one fan, it would go filter<fan<cooltube<exhaust.

250cfm or better

Did I cover it all? I smoked a few bowls and it crept up on me just now.

Use a 4" blower and a 6in carbon filter. A passive exhaust will not do ya

Yes you can use one fan, it would go filter<fan<cooltube<exhaust.

250cfm or better

Did I cover it all? I smoked a few bowls and it crept up on me just now.




Thanks, if I use 250cfm fan what size filter matches?

filters are sized by the diameter of the ducting - 4" , 6" or 8"

I'm new to building a grow room and I'm trying to understand the ventilation issues. When you set this up as filter<fan<cooltube<exhaust then presumably the filter end is attached to a duct that leads to a vent. Can the other end of the cooltube be left open and allowed to draw air from the room? If another vent was provided close to the light this could help ventilate the room. Would this work or should you run a duct from the light to a vent to draw cooler air from outside and handle the room ventilation as a separate issue? What would you suggest for room ventilation?