What Size Extractor Fan & Carbon Filter Do You Need? (Grow Tent Sizing Chart)
Undersize your extractor fan and you get heat spikes, mould-friendly humidity and smell leaks. Oversize it slightly and it runs quiet, cool and cheap. This guide gives you the exact answer for every tent size we sell — in about 30 seconds.
The 30-second answer: sizing chart
Find your tent, read across. The maths behind it: replace all the air once a minute, then add 25% because the carbon filter and ducting create resistance.
| Tent size | Volume | Airflow needed | Fan size | Our pick |
|---|---|---|---|---|
| 75 × 75 × 160 cm | 0.9 m³ | ~70 m³/h | 4" (100 mm) | RVK 100 on low |
| 100 × 100 × 200 cm | 2.0 m³ | ~150 m³/h | 5" (125 mm) | RVK 125 |
| 120 × 120 × 200 cm BEST-SELLER | 2.9 m³ | ~220 m³/h | 6" (150 mm) | RVK 150 / IsoMax 150 |
| 150 × 150 × 200 cm | 4.5 m³ | ~340 m³/h | 6" (150 mm) | RVK 150 on high |
| 120 × 240 × 200 cm | 5.8 m³ | ~430 m³/h | 8" (200 mm) | RVK 200 / Rhino EC 200 |
| 200 × 200 × 200 cm | 8.0 m³ | ~600 m³/h | 8" (200 mm) | RVK 200 / Rhino EC 200 |
| 240 × 240 × 200 cm | 11.5 m³ | ~870 m³/h | 10" (250 mm) | Rhino EC 250 |
| 360 × 240 × 200 cm | 17.3 m³ | ~1,300 m³/h | 12" (315 mm) | Rhino EC 315 |
Golden rule
Between sizes, always round up. A bigger fan on half speed is quieter, cooler-running and lasts longer than a small fan screaming at 100%. It also gives you headroom for hot summer weeks.
The formula (for any space)
Growing in a cupboard, loft or a room instead of a tent? Same calculation:
Matching the carbon filter
Two rules and you can't go wrong:
Match the diameter
A 6" fan takes a 6" filter — same flange size means no reducers, no leaks, no lost airflow.
Filter rating ≥ fan rating
Check the filter's m³/h figure is at least the fan's. If the filter is the bottleneck, the fan strains, gets loud, and odour scrubbing suffers.
Filters are consumables — the carbon saturates after roughly 12–18 months of running and the smell starts creeping through. If your filter is older than that, replace it before troubleshooting anything else.
Systemair RVK Fan
from £64.95
The reliable workhorse — quiet, efficient, lasts years
IsoMax Acoustic Fan
from £249.95
Whisper-quiet — insulated body for noise-sensitive spaces
Rhino Ultra Silent EC Fan
from £224.95
EC motor — most efficient, pairs with a digital controller
Rhino Pro Carbon Filter
from £49.95
Match the diameter to your fan
Noise: how to run near-silent
Extraction noise comes from three places — the fan motor, air rushing through ducting, and vibration passed into the frame. Fix all three:
Buy one size up, run it slower
The single most effective trick. A 6" fan at 60% moves the same air as a 5" at full tilt, at a fraction of the noise.
Go acoustic or EC
IsoMax fans have insulated bodies. Rhino Ultra Silent EC fans go further — the EC motor is near-silent at low speeds and a digital controller holds the exact speed (and temperature) you set.
Acoustic ducting + soft mounting
Insulated ducting muffles the air-rush; hanging the fan and filter on rope ratchets instead of bolting them to the frame stops the hum travelling through the tent poles.
Combi Ducting 5m
from £9.95
Acoustic Ducting 5m
from £19.95
Fast Clamps
from £2.95
Silver Duct Tape
£5.95
The right layout inside the tent
Hang the chain high inside the tent, back corner: filter → short duct → fan → duct out. Heat rises, so extracting from the top pulls the hottest air first. Keep duct runs short and straight — every tight bend costs you around 5% airflow. Fresh air enters through the bottom passive vents, sweeps up past the plants, and out through the filter.
Want it all matched for you in one click?
Our extraction filter kits bundle a correctly-paired fan, filter, ducting and clamps for each tent size — or browse all extractor fans and carbon filters.
Quick answers
What size extractor fan do I need for a 1.2m grow tent?
A 6" (150 mm) fan. A 120 × 120 × 200 cm tent holds 2.88 m³ of air; changing it every minute plus 25% for the filter and ducting means you need roughly 220 m³/h — comfortably inside a 6" fan's range, with headroom to run it quieter on a lower setting.
Do I really need a carbon filter?
If smell matters at all, yes. The filter scrubs odour before air leaves the tent, and it only works if ALL exhaust air passes through it — which is why it hangs inside the tent, first in the chain, and why the tent must hold negative pressure.
Should the fan and filter be the same size?
Yes — match the flange diameter (a 6" fan with a 6" filter). Check the filter's rated m³/h is equal to or higher than the fan's; a filter that's too small chokes airflow and the fan works harder and louder.
Is my fan too loud — what are my options?
Three fixes, in order of cost: run an oversized fan on a lower speed (buy one size up), swap to an acoustic fan like the IsoMax or a Rhino EC with a digital controller, and use acoustic ducting with a silencer. Soft-mounting the fan on rope ratchets rather than rigid brackets also kills vibration hum.
Where should air come IN?
Through the passive intake vents at the bottom of the tent — open roughly 3–4× the area of your exhaust outlet. If the tent walls suck in hard, open another vent; a gentle inward bow is perfect (that's negative pressure doing its job).
More grow guides
Guides on full tent setup, feeding in coco and spider mite rescue are landing here soon — browse all grow guides.
Questions? Call the shop on 020 3488 0419 — free expert advice, 6 days a week. Free UK delivery over £50, next-day available.
