Newb ventilation question - Fan and Carbon filter

Hey guys, so I have a newb question about grow tent ventilation. I have a 36" x 20" x 62" tent with a 250w hps. I was originally just gonna have two booster fans - one intake, one exhaut. The guy at the hydro store said I only need one good inline fan. He told me how to use it, but frankly I was a bit blitzed.

So I want the fan to suck air out? And then just leave another flap open for intake? And also what would be the best way to attach a carbon filter? He said that there's several ways to do it.

Edit:

Oh and I'm using a 4" Ecoplus Inline fan rated at 160 cfm.

The way I have my 4x4 tent with a 600w HPS is filter>hood>6 in inline fan>exhaust ducting out of tent. For intake I have a 4in inline fan sucking air from the bottom of tent. Lights on temps stay around 78F.

In my 5x5 tent i go filter>fan>hood>exhaust. My theory here is that negative pressure is sucked from the filter and then pushed through the hood. This causes less leaks that could carry odor

View attachment 1226853

This will be reworked slightly to be more effective, but all I'm going to do is try to cut out such a drastic bend in the duct... I'ma try and make it a 90 degree bend as apposed to a 180 degree

Filter>fan>ducting>hood>ducting out

I have a 8,000 btu A/C blowing air in through 6" insulated ducting at the bottom of the tent

Either of the prev posts will work. With a big enough inline exhaust fan an intake fan isn't necessary in that small area.
When sizing the fan here are some general suggestions,
To cool, you need enough CFM to exchange the air at least once per minute. 3-4 times is ideal.
The filter will add about 30% drag on the airstream, so take that into account for total fan CFM rating.
If you can put the filter outside the tent (light/fan/duct/filter) it will be quieter. Well, a little anyway.
Good luck,
Fred

BCcannabis said:

In my 5x5 tent i go filter>fan>hood>exhaust. My theory here is that negative pressure is sucked from the filter and then pushed through the hood. This causes less leaks that could carry odor

Click to expand...

TheRuiner said:

View attachment 1226853

This will be reworked slightly to be more effective, but all I'm going to do is try to cut out such a drastic bend in the duct... I'ma try and make it a 90 degree bend as apposed to a 180 degree

Filter>fan>ducting>hood>ducting out

I have a 8,000 btu A/C blowing air in through 6" insulated ducting at the bottom of the tent

Click to expand...

The problem with both of these methods is that you are exposing part of your system to odor leaks by running the hood through your exhaust! You are scrubbing the air at the begining, then pushing scrubbed air through a hood that more than likely leaks, then exhausting outside of tent. There are two problems with this.... odor control, and negative pressure control. The proper way to run a scrubber and a vortex is like this....

Air scrubber >> fan >> exhaust >>

That will take the warmer air high in the tent and exhaust it, free of odor if you dial in your FMs to match the rating on the scrubber. As for the hood, most tents have hood vents, so I run mine like this....

passive intake >> duct >> HOOD >> duct >> 160 FM inline fan >> exhaust

This way you are bringing cool air from the room the tent is in and you are drawing it across the hot bulb and exhausting it immediately.

This is the most efficient way at venting a grow tent in my opinion. Any flaws in my thinking?

fred flintstoned said:

Either of the prev posts will work. With a big enough inline exhaust fan an intake fan isn't necessary in that small area.
When sizing the fan here are some general suggestions,
To cool, you need enough CFM to exchange the air at least once per minute. 3-4 times is ideal.
The filter will add about 30% drag on the airstream, so take that into account for total fan CFM rating.
If you can put the filter outside the tent (light/fan/duct/filter) it will be quieter. Well, a little anyway.
Good luck,
Fred

Click to expand...

Using a fan to exhaust air through a charcoal scrubber is a no-no. For one, you'll kill the fan early on and two, the scrubber is designed to work oppositely, the odor is drawn into scrubber then scrubbed air is vented into duct to be exhausted. You have it backwards. Most scrubbers have CFM ratings. Use a fan controller and simply dial your fan down to match the rating. If you have a long run or several bends in duct, increase CFM slightly.

Serapis said:

The problem with both of these methods is that you are exposing part of your system to odor leaks by running the hood through your exhaust! You are scrubbing the air at the begining, then pushing scrubbed air through a hood that more than likely leaks, then exhausting outside of tent. There are two problems with this.... odor control, and negative pressure control. The proper way to run a scrubber and a vortex is like this....

Air scrubber >> fan >> exhaust >>

That will take the warmer air high in the tent and exhaust it, free of odor if you dial in your FMs to match the rating on the scrubber. As for the hood, most tents have hood vents, so I run mine like this....

passive intake >> duct >> HOOD >> duct >> 160 FM inline fan >> exhaust

This way you are bringing cool air from the room the tent is in and you are drawing it across the hot bulb and exhausting it immediately.

This is the most efficient way at venting a grow tent in my opinion. Any flaws in my thinking?

Click to expand...

I have heard this before but with positive pressure after the fan no leaks are possible. That is why the fan is attached directly to the filter, if any leaks occur after that they will blow the odor free air back into the tent.

If i am missing somthing than i would like to know more. So you run 2 fans? one for the filter and one for the hood? I ran this before but found it more noisey and one fan still does the job for me and works

It sounds like you know what your talking about S-man. I did'nt see cfm rating on my filter. How do you match a cfm rating though?
Say i have a 6" vortex 452cfm going into phresh 55. What speed should I run my fan on? Or how do I find out?

hoagtech said:

It sounds like you know what your talking about S-man. I did'nt see cfm rating on my filter. How do you match a cfm rating though?
Say i have a 6" vortex 452cfm going into phresh 55. What speed should I run my fan on? Or how do I find out?

Click to expand...

This link shows the CFM rating for different phresh filter sizes
http://www.phreshfilter.com/selector.php

Thanks for all the suggestions guys! All super helpful.

But I now have another super noob question - what exactly does "hood" refer to? Is it the attachment on some reflectors? My light is the basic one from HTG Supply. Does it have a hood?

Wrong wrong wrong

Wrong wrong

fred flintstoned said:

Either of the prev posts will work. With a big enough inline exhaust fan an intake fan isn't necessary in that small area.
When sizing the fan here are some general suggestions,
[To cool, you need enough CFM to exchange the air at least once per minute. 3-4 times is ideal.]
The filter will add about 30% drag on the airstream, so take that into account for total fan CFM rating.
If you can put the filter outside the tent (light/fan/duct/filter) it will be quieter. Well, a little anyway.
Good luck,
Fred

Click to expand...

You should strive to replace all the air in 2-4 minutes. If i needed to replace all the air in my, say 15 x 15 room, "3-4 times/ minute" I would need a fan rated at 7200 cfm. If I replaced all the air in this room once in 3 minutes I would need a 600 cfm fan. ya dig

A Hood is your reflective hood that your light should be hooked up to. A vented hood is almost always needed to keep the temps down while using a grow tent. Here is a picture of a hood similar to the one i use, its called a cool-tube, this allows for most of the heat generated from the light to be exhausted.

Do what the hydro store guy said. If you want to run a filter run it on a dedicated system. you'll need another fan. GL

chooi said:

Hey guys, so I have a newb question about grow tent ventilation. I have a 36" x 20" x 62" tent with a 250w hps. I was originally just gonna have two booster fans - one intake, one exhaut. The guy at the hydro store said I only need one good inline fan. He told me how to use it, but frankly I was a bit blitzed.

So I want the fan to suck air out? And then just leave another flap open for intake? And also what would be the best way to attach a carbon filter? He said that there's several ways to do it.

Edit:

Oh and I'm using a 4" Ecoplus Inline fan rated at 160 cfm.

Click to expand...

Mountainfarmer said:

You should strive to replace all the air in 2-4 minutes. If i needed to replace all the air in my, say 15 x 15 room, "3-4 times/ minute" I would need a fan rated at 7200 cfm. If I replaced all the air in this room once in 3 minutes I would need a 600 cfm fan. ya dig

Click to expand...

I agree with this too, but remember that too much ventilation is better then too little. IMO

Mountainfarmer said:

Do what the hydro store guy said. If you want to run a filter run it on a dedicated system. you'll need another fan. GL

Click to expand...

I have an extra 435 CFM inline fan that is just sitting around because i found that it was not needed. For a grow tent as small as yours you only need 1 fan, you will be fine with your 4" fan, you only have about 30 cubic feet in that tent. For bigger rooms i do think that the filter system needs a dedicated fan and the lighting system needs a dedicated fan.