Climate & Ventilation — Circulation Fans

A circulation fan solves two things your extraction leaves alone. It breaks up the still, humid layer sitting right against the leaf, and it makes stems grow against light resistance, which is what makes them sturdy. The choice here is not about power but about where you can fit it and what it blows at.

On the pole, inside the tent

Inside a tent a clip fan is the most practical, because it grips the frame and costs you no floor space. AC Infinity has the CLOUDRAY A6 and A9 with a fixed head and the S6 and S9 that oscillate. Garden Highpro ProFan clip fans come in 15 and 20 cm, and Fertraso has a 15 cm clip and table fan that also stands on a base.

Low draw, and why it matters here

The Secret Jardin Monkey Fan comes as a 180 mm version and as a 24 volt version, the latter also in a twin pack. A circulation fan runs all day, often several per tent, so its power draw counts differently from an appliance that cuts in occasionally. Two small fans keeping the air moving generally do more than one large one blowing at a wall.

For a room rather than a tent

Above tent size, Fertraso has floor, wall and pedestal fans from 30 to 50 cm, plus a 30 cm box fan. The Pro Deluxe versions in 45 and 50 cm come as wall, pedestal and rotating floor fans, with oscillation and a remote. A wall model is often the better choice here, simply because it takes no floor space and can be aimed above the canopy.

Aiming is the whole story

Never aim one straight at the tops at full blast. Sustained hard wind on one spot causes damage rather than strength: the leaf curls, transpires too fast and the plant closes its stomata. What you want is movement throughout the space, so blow along the canopy or at a wall and let the air circulate. Above and below the canopy are two different layers of air, and the lower one is the one most often forgotten.

Frequently asked questions

How many circulation fans do I need?
For a single tent, usually two small ones, one above and one below the canopy, rather than one large one. What matters is movement everywhere, not air speed at one point.

Does this replace my extraction?
No. A circulation fan removes nothing and lowers neither your temperature nor your humidity. You need both, and neither takes over the other's job.

Clip or pedestal?
Clip inside a tent, because it costs no floor and sits at the right height. Pedestal or wall for a whole room, where you have to move more air over a greater distance.

Should it keep running at night?
Yes, especially then. In the dark period temperature drops and moisture lingers, and that is exactly the situation where still air turns into mould.