Ducting Size Question for 3x3x6.5 Grow Tent

Hi,

I have a grow tent which is a 3x3x6.5 model. I've just ordered a 600 watt cool tube and need to get some ducting for it. The challenge is what size to buy. My set up looks like this:

Fan – 5”
Port holes – 5”
Carbon filter – 4”
Cool Tube – 6”

Three different sizes I know, kind of sucks....I suppose my choices would be to either cut a larger hole in the tent and go for 6” ducting, or use reducers and go 5”. I can't really afford to buy another fan and filter just now. My question is would there be a big difference as far as ventilation between 5” flex and 6” flex? I am new to this and need to decide something pretty quickly, so any advice you could offer would be great.
Thanks.

The difference between 5 or going to 6 is a matter of how fast or slow and how much static pressure you want the air to have. A bigger duct, with the same amount of airflow will give you LESS static pressure(good thing) and LESS velocity(also good thing for noise). A smaller duct would do the reverse.

In this example say you run 400CFM through a 5 inch it'll be going through at about 3,000 FPM and the static pressure will be about 3" over 100 ft.

Take that same 400 CFM and run it through a 6 inch and itll be going at 2,050 FPM and 1.1" of static pressure. You only dropped a third in the velocity part, but you dropped 2/3's in the static pressure(which is a big thing to consider). A higher than anticipated static pressure can give you less air flow and really stress your fan.

You never mentioned airflow of your fan. If it's less than 250CFM go 5" if its higher than go with a 6"

Since there was no mention of 2 fans I assume you're going: Carbon>4to6 reducer>cooltube>6to5 reducer>fan>5to6 reducer or straight 5 out depending on your fan size.

That fan is going to be CHOKING. I can only imagine its under 250CFM as few manufacturers are going to design a 5 inch fan that would do more. I know my cheapy 240CFM is a 6"

Good Morning,
Thank you for your response. What I am currently using is one mixed flow inline fan, 162 CFM. I am sorry I neglected to say that. At the time I bought it I was only going to run a 250 HPS light, which is what I am using now. It seemed to be a good option at the time. I have a medical referral but I still want to be a good neighbor and not alert anyone. This fan is pretty quiet. Yes I was going to try and run it through the cool tube once it arrives. I guess that must have been a bad idea. So do you think I should buy another fan? Could I keep the 4 inch filter or should I get another one of those as well?

If I were to keep the fan/filter I have now, in place, would it work to pick up a combo just for the light? I'm thinking in this case it may have to be as powerful (440 CFM). Although I don't know how powerful it would have to be.

Do you know the rated airflow for your filter?

I'd use the 162 cfm pulling air thru the cooltube and find something for the filter. For instance my filter is rated for a 400-550cfm fan. So I got a fan that put out that much. And to be honest 162CFM is small for an exhaust fan, nevermind a cooltube fan AND an exhaust fan. It'd cool a 250 HPS nicely though.

You're on the right track with a mixed flow inline. I was worried it was an axial. I still think its too small for that size of a tent.

Yes I like the fan, very quiet. I guess I wasted some money there though if I can't use it. My 4" filter recommend air flow is 150-256 CFM max.

How powerful of a fan would I need if I were to use my current combo for the tube? My tent is 3x3x6.5. Would you cut a larger vent hole in the tent or use a 6-5 reducer once the 6" flex reaches the tent wall?
Thanks for the help

5" ports suck to work with and is the problem when working with cheapy tents. That and the number of ports.. How many ports you got?

I'd run two systems. Use the fan you got currently for the cooltube and get another of the same or something a bit more powerful for the filter. If you can afford it. The one you got currently MIGHT be enough to do it all, but its a lot of static pressure to overcome. I'd only do it if u had 1 port.

Id reduce the cooltube to 5" and run that out. 5" round duct at 160cfm is .5" static pressure over 100ft and 1,200 FPM.

I'd use something between 200-250 for your filter.

What I've decided to do is sell my current fan and filter on ebay. I'll then buy a 440 cfm 6" Fan and compatible 6" filter, and open up one of my 5" holes on the tent to 6" via flange. One size fan filter and light, keeping things simple. Hey, I wanted to thank you for taking the time out to run those numbers by me and give me some options to consider. You take care now......
Kieth