[PC Grow] Problem with filter, air flow direction and temperature

Hello! I am building my first PC grow box, I am in the testing phase and I have a problem. My grow box contains 2 chambers, one for the growing area and a small one for the electrical stuff (powerbar, wiring...). There is a wooden separator between the 2 chambers and it has a hole on which I attached a 50CFM PC fan (blowing from the grow chamber toward the electrical chamber) and my DIY carbon filter (the filter is on the electrical side). I have another 50CFM PC fan on the electrical side blowing the air out of the case. The intake is in the grow chamber and is passive (no fan or anything, as per the recommendations online).

The problem is that the flow of the fan blowing through the filter seems to "invert" as soon as I attach it to the filter. I tested the direction of the flow by passing a zippo lighter through my grow chamber and it seems to be really turbulent. Sometimes, the flames goes toward the exhaust fan and sometimes it goes in the opposite direction. I think this results in air not being exhausted properly which in turn makes the grow room really hot. The temperature stays between 90F to 95F...

I have 3 23W CFLs, the grow chamber dimensions are about 14"x7"x17". I was thinking about removing the filter and trying to use only ona gel for the odor but I am a bit worried about this solution. I also tried adding another fan inside the grow chamber pushing the air to the exhaust but it didn't help that much. Do you have any suggestions as to what I should try to fix the problem?

Thank you very much!

I'm having some heat issues myself.


I had 4 fans.
2 in and 2 out.

Today i just moved it so i have 3 out and 1 in. Hopefully it works.

I also removed 2x 23w cfl and.changed.those for 16w

I would try just the ona and see.of that helps. Depending how u made your filter it could.be blocking the air or atleast restrict it enough

I put two 92mm AC fans in series about 2.5 inches apart in a little square tube that forces air through my scrubber. My mini-fridge stays about 3-4 degrees above room temperature, with a 150W of LED light pulling about 100W. I recently had a problem with my grow box getting too cold because I was cheap and not running the heat in the house lol.

When I originally used one fan, I could feel air blowing back through the fan like you described. Now, the second fan pushes it back in and I run nice negative pressure.

I'm in the process of building a grow box at the moment (stereo speaker). My speaker has two identical holes in the front, one with a tube for the woofer, and another for the tweeter. I moved the tube to the tweeter hole at the top, and plan on using this as my exhaust w/ carbon scrubber. From what I've read concerning air flow and filters, it's easier to pull air through the filter than to push it. And doing both has a couple advantages. Apart from increased airflow, it should also allow you to run them at lower speeds --less noise-- and still have more CFMs moving than with a single fan.

As I think about it, I'll probably mount a fan right on the tweeter hole, and have the tube be the filter, with another fan pushing the air through.

stone604 said:

I'm having some heat issues myself.


I had 4 fans.
2 in and 2 out.

Today i just moved it so i have 3 out and 1 in. Hopefully it works.

I also removed 2x 23w cfl and.changed.those for 16w

I would try just the ona and see.of that helps. Depending how u made your filter it could.be blocking the air or atleast restrict it enough

Click to expand...

Yes, I think I will have to try something else for the lights unfortunately

mc130p said:

I put two 92mm AC fans in series about 2.5 inches apart in a little square tube that forces air through my scrubber. My mini-fridge stays about 3-4 degrees above room temperature, with a 150W of LED light pulling about 100W. I recently had a problem with my grow box getting too cold because I was cheap and not running the heat in the house lol.

When I originally used one fan, I could feel air blowing back through the fan like you described. Now, the second fan pushes it back in and I run nice negative pressure.

Click to expand...

Thanks, I will try that!

MrVanker said:

I'm in the process of building a grow box at the moment (stereo speaker). My speaker has two identical holes in the front, one with a tube for the woofer, and another for the tweeter. I moved the tube to the tweeter hole at the top, and plan on using this as my exhaust w/ carbon scrubber. From what I've read concerning air flow and filters, it's easier to pull air through the filter than to push it. And doing both has a couple advantages. Apart from increased airflow, it should also allow you to run them at lower speeds --less noise-- and still have more CFMs moving than with a single fan.

As I think about it, I'll probably mount a fan right on the tweeter hole, and have the tube be the filter, with another fan pushing the air through.

Click to expand...

Good luck man, I hope you don't end up like me with a completed box that's too hot hahaha!

fuckthisinsaneshit said:

Good luck man, I hope you don't end up like me with a completed box that's too hot hahaha!

Click to expand...

Well, the speaker isn't too small: 7.75"x10"x28" (LxWxH) Those are the inside measurements. I plan on using a scrog, and using as much of the height as I can.

You may also want to take a look at how dense the filter is. If there is too much material then airflow may not be possible with the fans you are using. Take the fan that is pushing air through the filter and turn it around so it is pulling the air through the filter and out of the case.

Also, heat rises so it is easier to remove from the top of the case. Make sure your filter/fan is as close to the top of the case as possible. that is why I am using the hole at the top of the speaker. The lights will be underneath it, so the heated air will rise toward the exhaust fans.

Similarly, cold air is easier to move into the case from the bottom. If you had a fan at the bottom of the case pushing cool air in that would also help. Even if you didn't have a fan, but allowed air in through the front of the case, your temps would probably drop a bit.

Some pictures would probably help us help you.

I think the problem is the filter thickness, yes. I do have it at the top of the case and the intake at the bottom. I don't have pictures right now, I will post them later. Thank you!

Pics would be great. I'm sure you can get your temps down.