How to install a carbon filter in a grow tent
Updated: October 2026
The parts are on the floor: a tent, an inline fan, a carbon cylinder and a coil of flexible duct, and the job is to join them so the tent holds a slight vacuum and the smell leaves outdoors. This is how to install a carbon filter in a grow tent once you have already chosen the SKU. Product rows are on the [carbon filter grow tent comparison](/hub/raised-beds-greenhouses-and-compost/carbon-filter-grow-tent). A qualifying purchase can earn a commission at no extra cost to you. Herbs and seedlings are the examples here. Cannabis cultivation still needs a Home Office licence, and a tidy duct run does not supply one.
The parts are on the floor: a tent, an inline fan, a carbon cylinder and a coil of flexible duct, and the job is to join them so the tent holds a slight vacuum and the smell leaves outdoors.
The parts are on the floor: a tent, an inline fan, a carbon cylinder and a coil of flexible duct, and the job is to join them so the tent holds a slight vacuum and the smell leaves outdoors. This is how to install a carbon filter in a grow tent once you have already chosen the SKU. Product rows are on the carbon filter grow tent comparison. A qualifying purchase can earn a commission at no extra cost to you. Herbs and seedlings are the examples here. Cannabis cultivation still needs a Home Office licence, and a tidy duct run does not supply one.
Our top picks
| Badge | Product | Duct | Weight | Pre-filter | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  AC Infinity AC Infinity 100 mm carbon filter | 100 mm | 2.48 kg | Yes | 9.0 | about £47.99 | View offer |
| Best value |  AC Infinity AC Infinity 150 mm carbon filter | 150 mm | 4.63 kg | Yes | 9.0 | about £65.99 | View offer |
 AC Infinity AC Infinity 150 mm fan kit | 150 mm | 11.9 kg | n/a | 5.5 | about £189 | View offer |
On this page
Before you clip anything
Lay the fan, the filter, the duct, jubilee clips and the pre-filter sleeve in the order they will sit. Check that all three diameters match. A 150 mm fan, a 150 mm filter and 150 mm duct is the set UK guides prefer for a typical 120 cm tent. A reducer is the part to put back in the drawer. Diameter maths sits on the size guide.
The fan should meet a BS 1363 socket on a 230 V ring. London Fire Brigade advice on leads is to avoid piled adaptors and to unwind a cable drum so the flex can shed heat. If the socket is scorched, or the board trips when the lamp and the fan start together, stop and use a qualified electrician. The AC Infinity 150 mm filter weighs 4.63 kg, and the CLOUDLINE LITE kit is listed at 11.9 kg. Strap the cylinder so it does not sag the roof.
Mount the fan and run the duct
Mount the inline fan first, on the tent collar or a shelf, with the cable strain relief clear of hot lamps. Fit the flexible duct with a jubilee clip at each end and tighten until the duct cannot pull off by hand, without cutting the plastic. Pull the flex out so it is as straight and as short as the room allows. A crushed coil behaves like a blocked pipe: the fan gets loud and the tent never quite pulls in.
Greens Horticulture’s sizing article also mentions a back-draft shutter on the outdoor side so wind does not push cold air back through the carbon when the fan stops. Fit that at the weather end, not inside the carbon bed. Keep the outdoor exit clear of a neighbour’s window.
Attach the filter the right way round
The carbon filter sits so the full airflow passes through the bed. On a tent that pulls air out, growers usually hang the filter inside the tent and let the fan draw through it, then send duct outdoors. You can place the filter on the exhaust side of the fan if the seals are tight and the arrow on the fan matches the direction of travel. Either arrangement works when there is no gap at the flange. A gap whistles and carries untreated air around the charcoal.
Look for the airflow arrow on the fan housing and line the filter’s open flange to it. Clip, then tug. Leave the pre-filter sleeve off until the metal joint is made, then fit it so it covers the mesh and does not block the flange. Two beds in series choke airflow.
Pre-filter, first run, and the date on the duct
Fit the pre-filter sleeve before the fan runs. Mars Hydro, Hon&Guan and AC Infinity bullets in this comparison mention one. Dust that reaches the charcoal shortens the bed. Write the install date on tape around the duct. UK shop blogs use twelve to eighteen months of continuous running as a replacement rule of thumb, and the pre-filter often needs a wash or a swap sooner.
Start the fan on its lowest speed. Close the tent most of the way and watch the walls pull in slightly. That negative pressure means leaks are not winning. A cold jet at a clip is a loose seal. If the tent balloons, the fan is pushing the wrong way. Do not recirculate paint or solvent fumes indoors. A UK review of the AC Infinity 100 mm filter reported black soot from that use.
When you should stop and get help
Stop if the plug runs hot, if a breaker trips when the fan and the light share a socket, or if the only exhaust path is a hole through a wall you do not own. Stop if you are about to use the tent for a controlled drug crop. The Misuse of Drugs Act 1971 does not bend around a quiet fan. A qualified electrician is the right call for scorch marks and new wiring. You can finish clips, sleeves and a leak test yourself when the socket and the exit already exist.
Common questions
Does the carbon filter go before or after the fan?
On a tent that extracts air, the usual place is inside the tent, with the fan pulling through the filter and the duct running outdoors. The filter can sit after the fan if every joint is sealed and the fan arrow matches the flow. Untreated air leaking around the flange misses the carbon either way.
How tight should the duct clips be?
Tight enough that a firm tug does not pull the duct off the flange, and not so tight that the clip cuts the plastic. Fully extend the flex first. A crushed coil will leak and roar even when the clip is perfect.
When do I fit the pre-filter sleeve?
After the metal joint is clipped, and before the first run. The sleeve catches dust that would otherwise load the charcoal. Listings for Mars Hydro, Hon&Guan and AC Infinity in this set mention a pre-filter. Wash or replace it when it looks choked, which is often sooner than the carbon itself.
Can I run the tent without exhausting outdoors?
You can move air, and you should not expect the carbon to make recirculated air clean. A UK review describes black dust when a filter was used on indoor paint fumes. Prefer an outdoor exit. If the building will not allow one, reconsider the tent rather than recirculating odour and dust into a bedroom.
Can I join a 4 inch filter to a 6 inch fan with a reducer?
You can, and UK duct guides advise against it. The reducer adds resistance, and the smaller bed sees air it was not rated to slow down. Match 100 mm to 100 mm, or 150 mm to 150 mm, which is the point of the rows on the comparison.
When should I call an electrician?
Call one for a hot plug, scorch marks, a breaker that trips with the fan and lamp together, or any new circuit. Everyday set-up stops at an existing BS 1363 socket. Wall cores and tenancy breaches are a landlord or building question, not a fan question.
Related pages
Sources
Public UK sources for sizing, licensing and electrical safety, last checked on 20 October 2026. Amazon.co.uk listing lines are the price and review source for the eleven ASINs. No laboratory odour test was run.
- Greens Horticulture — grow tent fan and carbon filter size (retrieved 20.10.2026)
- Hydroponics UK — carbon filter sizing guide (retrieved 20.10.2026)
- The Growers Shop — grow room ducting size guide (retrieved 20.10.2026)
- Roots2Riches — extraction fan calculator (retrieved 20.10.2026)
- Misuse of Drugs Act 1971, section 6 (retrieved 20.10.2026)
- GOV.UK — cannabis licensing factsheet (retrieved 20.10.2026)
- Electrical Equipment (Safety) Regulations 2016, regulation 35 (retrieved 20.10.2026)
- London Fire Brigade — cables, fuses and leads (retrieved 20.10.2026)