Help with ventilation system

Hey, I'm close to setting up my first growbox, but I need some final tips!
The dimensions are 3.5 x 3.5 x 6.5 and it will have a single 600W HPS.
I've calculated that I need about 450 CFM (please correct me if I'm wrong).
So here are my questions:
-Is the system in the picture good?
-Do both intake and outtake fans have to be 450CFM or 225/225?
-Or is it better to have only one 450CFM outtake fan with passive intake?
Thanks

You don't need 450 CFM but you could use it.
I would suggest getting a 4'' inline fan(around 200 cfm) or if you want to run your fan slower to be less noisy you can get a 6'' and get a speed controller. That way you could also turn up the fan and have a high CFM exhaust if ever needed.

As for the layout, you have it wrong. This is how you should do it.

newguy123 said:

You don't need 450 CFM but you could use it.
I would suggest getting a 4'' inline fan(around 200 cfm) or if you want to run your fan slower to be less noisy you can get a 6'' and get a speed controller. That way you could also turn up the fan and have a high CFM exhaust if ever needed.

As for the layout, you have it wrong. This is how you should do it.

Click to expand...

Thanks, so I don't need an intake fan, right? Also, Isn't your picture just like my layout? Carbon > fan and out?

Look up passive intakes

No air intake fan is needed


Just make your air intake size twwwice the area of the exhuast size

deFFciU said:

Thanks, so I don't need an intake fan, right? Also, Isn't your picture just like my layout? Carbon > fan and out?

Click to expand...

No you don't need an intake fan unless your lacking pressure but I don't think that would be your case.
Also the layout should be Iike this

Exhaust fan pulling, then the light and finally the carbon filter.

Edit: you always wanted to the fan to pull and not to push the air, as the fan is much stronger at pulling than pushing. Also you want to minimize the ducting you have. The shorter the better. More ducting is more work for the fan.

newguy123 said:

No you don't need an intake fan unless your lacking pressure but I don't think that would be your case.
Also the layout should be Iike this

Exhaust fan pulling, then the light and finally the carbon filter.

Edit: you always wanted to the fan to pull and not to push the air, as the fan is much stronger at pulling than pushing. Also you want to minimize the ducting you have. The shorter the better. More ducting is more work for the fan.

Click to expand...

Will there not be any unfiltered air though? Because the fan isn't pulling the air directly from after the filter, but from the lamp

You'll remove more heat from the bulb with your duct work hooked up to your hood then filter like the pic.

But you'll need to tape up your hood.Around the glass,any where there is a spot for air to pass through.

deFFciU said:

Will there not be any unfiltered air though? Because the fan isn't pulling the air directly from after the filter, but from the lamp

Click to expand...

In that setup, the air is being pulled through the filter first. Which then travels through the light and makes its way to the fan and exhausted out. An ideal setup, if you want to use your light as part of the exhaust to keep it cool.

As newguy stated, the more ducting and bends in your duct work will force you to lose cfm causing your fan to potentially struggle. IMO, always better to go with more than you need for reasons like this.

Whatever layout you decide, based on your actual diagram, hug the fan as close to the top as possible. You'll have to have as much height as you can to allow plant growth and not run into issues with that.

Here's my setup for an example. Due to lack of space, I didn't use any duct and no need to cool my lights because their LED and produce less heat. As you can see though, I hugged the fan/filter as close to the top as I could.

in my experience a 600watt in that size tent a aircooled hood is a must.
I had my filter hung from the roof.
then down to the hood and out.

I have my fans mounted outside the tent.

Looks good to me but make sure your carbon filter is rated higher than your fan CFM. I got myself a 600CFM filter to use with a 430CFM fan that I plan to run at half speed. The slower the air passes thru the carbon will do the best job for taking out the stink.

I've used my intake fan maybe a handful of times in the last 3 years, so no.

Also you won't run you 450 cfm at max often, you'll probably want a fan speed controller too
- good luck

Beachwalker said:

I've used my intake fan maybe a handful of times in the last 3 years, so no.

Also you won't run you 450 cfm at max often, you'll probably want a fan speed controller too
- good luck

Click to expand...

I've never used a fan on my intake. The deal there is to have twice as much intake space as exhaust. A 6" exhaust is about 20 square inches, (6 x pi) so 40 inch square for the intake will be fine. Can be multiple holes or a couple bigger ones as long as they add up to 40. Less if you want some negative pressure when the exhaust fan kicks in. I can barely get the door shut if the fan is on full when I'm leaving.

deFFciU said:

Will there not be any unfiltered air though? Because the fan isn't pulling the air directly from after the filter, but from the lamp

Click to expand...

That's arguably the best way, but you want your filter at the top to pull the hottest air out

Carbon filter on roof

short ducting into the light (in through the bulb side and out the fixture side is best)

Ducting out of the tent to the fan, then to exhaust

Beachwalker said:

I've used my intake fan maybe a handful of times in the last 3 years, so no.

Also you won't run you 450 cfm at max often, you'll probably want a fan speed controller too
- good luck

Click to expand...

Forgot to mention that I have a RH/Temp and speed controller on my exhaust fan. It only kicks in when it's told to.

Beachwalker said:

That's arguably the best way, but you want your filter at the top to pull the hottest air out

Click to expand...

I'm not so inclined to think that way. I have a 12-16" oscillating fan mixing up the air in my grow room and the temps are pretty much the same from floor to ceiling so fan/filter placement isn't dependent other than where it can fit easiest. I'm not in a tent tho and for most tents it fits best up at the top behind the light(s). Still should have lots of air movement in any grow space tho.

I always leave it on, 1600 watts of exhaust helps heat my bedroom on the other side of the wall 8 months of the year here in chilly New England lol, and in the summer it's not only always on but that's when I tend to turn it up and that's when I've also used the 220 inline can filter, but it doesn't do much if anything that I've noticed and I wouldn't buy it again if I had to do over