HELP! Air circulation & Fans

[Murf]

Hi guys.

I’m totally new to this, so excuse the noob question.

I now have a small tent setup in a spare room with a King LED 1200 light. Going for the Coco, Perlite mix. So I’m nearly ready to go for my first ever grow.

However, I would love some advice on the use of fans. I’ve given the light a run for a couple of days just to get an idea of heat in the tent before deciding on size of fan etc. However, the tent is running at about 74F (23.5C), which is cooler than I thought it would be.

I had been thinking of a 6” fan, but now I might go for a 4” extraction and just have a bottom vent open, with an oscillating fan inside, as I’m concerned that the tent will end up being too cold. Does this make sense or am I going the wrong way?

Also, how much smell is there from a small grow tent? Is it best to have a carbon filter to avoid the whole house stinking, or is the smell not too bad/strong?

Any advice would be very welcome 🙏🏻

Thanks
Kieran

[Murf]

Just to note, I’ll be growing Dutch Passion Blue Auto Mazar to begin with.

[madams9]

I went with a 4" system in my small tent. It is more than adequate. I had an oscillator in there and it failed. I concluded that the oscillating fan was important for a big plant to help it developed vertical strength, but ultimately it was too much plant for a small tent. Plant was supposed to be an auto flower, turned out to be be a full-size photoperiodic variety.

Plant was a challenge for the small tent, but it worked out. At any rate, if you're looking at fresh air circulation, 4" should be fine.


Just my 2¢.

[s62]

My advice: go for the 6” fan for exhaust. Better to have too much power than not enough. You can always use a fan-speed controller to turn the fan down. Plus, it’s quieter to run a big fan slowly than it is to run a small fan fast.
And yes, the smell can be very powerful. If discretion is needed, I’d definitely get a carbon filter.

[az2000]

One possible problem: Focusing on heat management, you might not move *enough* air. I once read that the entire volume of a grow space should be replaced every 5 minute (as a minimum. More frequently if you need to extract heat.). You can buy a hand-held CFM meter. Or, do the math to calculate 1/5th of your tent's cubic feet (the amount to exchange in one minute, convert that to gallons, and then use a large 40-gallon outdoor trash bag on the end of the exhaust tube to time how long it takes to inflate. Correlate that to the gallons you need to extract in one minute.).

That sounds tedious. But, it is possible to not extract enough air if you're trying to conserve heat. In that case, it might be better to use a less efficient light to have more heat.

Also, instead of stepping down to a 4" fan, you can use a 3amp variac with a 6" fan to slow it down). Variacs cost about $70 USD. They're not cheap. But, last forever (if you don't overload it with something drawing more amps. 3amp should be fine for a fan). I like variacs because they're extremely quiet. The inexpensive dimmer-like speed controllers have a reputation for causing fans to buzz/hum when dialed down to low speeds. Some people may notice it more than others. I notice it *a lot*, and love my variac because it's whisper quiet.).

If you go down to a 4" and run it at full speed, you'll hear it *much* more than a 6" dialed down to 25% speed. The latter, you'll hardly hear it. The former: it's going to sound like rushing air.

[Gluteous]

The purpose of the exhaust fan is to push warm air out of the tent THROUGH A CARBON FILTER (requirement!) and also to pull fresh air in. The fresh air in is vital. Your fan CFM should be enough to completely exchange all the air every 3-5 minutes. As noted up top, a 6" running slower is better than a 4" running faster. You'll want a fan speed regulator if the fan doesn't come with one.

Purpose of the oscillating fan is air movement. Duh. But the benefits are strengthening the plants and it helps with pest/disease control. Mold spores and bugs have a harder time landing with good airflow.

74 degrees may not be ideal but it's totally fine. Like Nebula says, if the temp is comfortable for you, your girls will like it too.