Too much air flow?

[Dingo84]

Hi guys,
just need some help I have a small grow box 2ft x 2ft x 6ft and I have just bought and installed a 6inch inline fan, after realising how much noise it makes and how powerful it is I bought a fan speed controller, however when I turn the fan speed down the inline fan makes a buzzing noise in the fan motor just as loud and annoying than the noise of the fan at full speed. I did the math and I think I only need to move around 30cfm, the 6 inch fan moves 350cfm.

Am I harming my plants by running a fan that is circulating a lot more air through the area than is needed?

I have just looked online and I should have got a 4 inch fan it only moves around 120cfm. But I will not have the money to get one for a couple of weeks now.

Does anyone know why the motor on the fan makes a buzzing noise when I turn the fan speed down? Can this be fixed somehow?

Also does anyone recommend PC fans intake and/or outtake fans for this size area or are they a waste of time or ineffective.

All feedback appreciated.
Thanks

 

[JuanCarlos]

In general I don't see anyone recommending computer fans for a grow space, usually you only see them used on small stealth setups and dry boxes. Your setup is 24 cubic feet which is relatively small. They say that you want to exchange the total volume of air in your space (24 cubic feet) once every 3-5 minutes. That means you need a fan that pushes 5-8 CFM based on that math. A computer fan might do it, but I would grab a 4" duct booster fan which can be had for less than $30 and hook that to your controller. You could experiment with a computer fan, just not sure how well they can pull air from a larger enclosure. And a passive intake will be just fine, no need for a fan there.

 

[Cannabliss89]

Yea if you were to run that fan at full power it would be way to much, it would replace the air like once every 5 seconds. You want to replace the air once every 2-5 minutes, some people say anything faster than once per minute is putting stress on the plants. Even if you have that 350cfm fan on the lowest controller setting it will still be too much. The 120cfm running at the lowest controller setting might be ok, I'm not sure how much those controllers reduce the cfm. You want a fan running at around 10cfm, but that's without a filter. Do you have a carbon filter attached to your vent setup?

 

[madsdad4ever]

man as long as u r not mangling the leaves then u r ok u can never have too much air lol u should check out my journal i have a smaller space then u and i am running a 1/3 horse power home ac fan i probaly change the air like a 100 times a sec i am using a lamp dimmer switch as a speed controller on that fan it tends to make a hum too when i have it turned down

 

[Dingo84]

Thanks for the replies, the 4 inch booster fan sounds like a good option, unfortunately they're sold out at the moment in aus so I have found a 100mm axial fan eBay. Do u think this will do the trick? Even though I have been reading that too much air flow would not be the worst thing for the plants so long as it's not tossing them around the room, but it's just too noisy.
Worked a treat drying my soil quicker though which was a problem I had before with poor air flow.
Thanks again appreciate the support

 

[Cannabliss89]

Yea you could try that fan. N yea as long as your not giving your plants wind burn then they'll probably be ok but it's just unnecessary. There's no benefit to exchanging the air more than once per minute, your plants could get dehydrated and your soil is going to dry out faster, not to mention the waste of money in electricity.

 

[Dingo84]

Hi can someone please help,
I have a 80cfm axial fan at the top for air exhaust in an area of about 40cfm,
2x 4" passive air intake holes at the bottom.
The axial fan doesn't seem to work that well as an exhaust fan as I don't feel too much suction when I put my hand near it to feel the pull.
I have quite high humidity of about 60-75% during early flowering stage and want to sort it out quickly.
Does anyone know if it would help if I block one of the passive airflow holes will that promote more intake draft from the open intake and in turn create better airflow through the set up?
I know I need a different (better) exhaust fan but won't be able to get one just yet.

 

[Fuzzy Duck]

Ye a 6 inch fan is more than enough for that space a 4 inch would more likely do the job...

How ever as you have fan speed controller i may adjust that to see if that reduces noise level, adjusted to 40% to 60% i suspect that may help... it is mainly the bearings in the fan which don't like the lower speed

 

[Fuzzy Duck]

As for noise you may wish to try fan silencers or at least acoustic/muffled ducting as another suggestion.