Circulation is the air job most growers underbuy, because it doesn't remove anything b it just stirs the air already inside your tent. But that stirring is a real growing input: it thickens stems, breaks up the damp pockets where mould starts, and keeps your leaves feeding. Here's the gear that does it, how to set it up, and why a circulation fan is not the same thing as your extraction.
The quick answer
- Clip fan - the workhorse: small, oscillating, clamps to a pole or bar, points across the canopy
- Floor / pedestal fan - for bigger tents and grow rooms, more air over a wider footprint
- Intake + exhaust - a separate job: that's air exchange, not circulation (more on this below)
If you want one answer: a small oscillating clip fan sorts most tents up to 100 x 100cm, and they start around €18 - €24. Step up to a second clip fan or a floor fan once your canopy fills out.
What fan do I need for air circulation in a grow tent?
For most tents the answer is an oscillating clip fan. It clamps to a tent pole, sweeps side to side, and pushes a gentle breeze across and up through the canopy. One down low blowing across the pots covers a 60 x 60 or 80 x 80 nicely. In a taller tent, add a second clip fan at mid-height so the lower leaves don't sit shadowed in dead air. For a 120 x 120 or a walk-in grow room, a floor or pedestal fan moves more air over a wider area.
We stock clip and oscillating circulation fans across the sizes most Irish growers need - the small oscillating clip fans are what most beginners walk out with. Browse the full fan range here.
Why does air circulation matter?
A plant outdoors gets worked by the wind, and that stress tells it to build thicker, woodier stems strong enough to hold up the canopy on their own. A plant in still indoor air skips all that - you end up with celery: long, thin, hollow stems that fold over the moment the buds put on weight, leaving you tying everything up with canes. A moving fan fixes that, and does two more jobs: it scatters the pockets of warm, humid air around the leaves where mould takes hold, and it refreshes the thin still layer of CO2-depleted air right at the leaf surface so the plant keeps photosynthesising. That's why circulation counts as a growing input, not just comfort.
Where should I point the circulation fan?
Point it across and up through the canopy, not straight down like a hairdryer and not pinned on one plant. The rule we give people at the counter is simple: leaves should rustle, not flap. If they're visibly flapping or the plant leans away from the fan, it's too close or too strong - back it off. Position it low, blowing across and up; add a second small fan at mid-height in a tall tent. You're after gentle pressure waves that flex the stem, not a gale.
Is a circulation fan the same as an extraction fan?
No! And this is the bit that trips beginners up. They do completely different jobs:
- Circulation (clip / oscillating / floor fan) moves air around inside the tent. It removes nothing. Job: stem strength and stopping stagnant, mouldy air.
- Extraction (inline fan pulling through a carbon filter, plus a passive or active intake) exchanges the tent's air with the room - pulling out heat, humidity and smell and bringing fresh air in.
You need both. Extraction sets up your intake and exhaust so old air leaves and fresh air arrives; circulation keeps that air from going stagnant around the plants in between. Skipping circulation is how growers end up with floppy stems and surprise mould in a tent that's otherwise well extracted. If you're sorting your extraction at the same time, our inline fans and carbon filters are sized by tent volume.
When should the circulation fan run?
Run it during lights-on, all day - that's when the plant is transpiring and photosynthesising and benefits most from moving air. Many growers leave a gentle circulation fan ticking over during lights-off too, on a lower speed, to keep humidity from settling in cold corners. Your extraction runs on its own schedule or thermostat; the circulation fan is the simple one.
Pop in and we'll set your airflow up with you
If you're not sure how many fans your tent needs, tell us your tent size and plant count - we sort this every day at the shop. DIG is Ireland's largest grow shop, based in Dublin, with collection available in store.
Want the full science behind it - boundary layers, wind stress and why stems thicken? Our friends at Grow Good Bud have the free in-depth guide.
FAQ
What fan do I need for air circulation in a grow tent?
For most tents up to 100 x 100cm, a small oscillating clip fan does the job. Add a second clip fan at mid-height in a taller tent, or step up to a floor fan for a 120 x 120 or a walk-in grow room.
Where should I point the fan in a grow tent?
Across and up through the canopy, not straight down and not aimed at one plant. The leaves should rustle gently - if they're flapping, the fan is too close or too strong.
Is a circulation fan the same as an extraction fan?
No. A circulation fan stirs the air inside the tent for stem strength and to stop mould. Extraction (an inline fan with intake and exhaust) exchanges the tent's air to remove heat, humidity and smell. You need both, doing different jobs.
Does air circulation actually improve growth?
Yes. Gentle moving air strengthens stems through wind stress and refreshes the depleted air at the leaf surface so the plant keeps feeding on CO2. It's a growing input, not just comfort.
Where can I buy circulation fans in Ireland?
DIG (Dublin Indoor Gardening) stocks clip, oscillating and floor circulation fans plus intake and exhaust kit, with collection in Dublin and delivery across Ireland.