The AC Infinity Air Filter Box, 100 mm is an inline filter housing that sits in a duct run and takes the dust, dirt, pollen and lint out of the air before it reaches the space. It is built from 1 mm cold-rolled steel with aluminium duct flanges and a matte black powder coat, and it is designed for intake applications — filtering the outside air a fan is pulling in, rather than cleaning what is already inside the room.
It fits 100 mm (4″) ducting and pairs with the CLOUDLINE PRO S4 or CLOUDLINE PRO T4. Because a pleated filter adds resistance, a high static-pressure mixed-flow fan is what keeps real airflow up once the box is in the run.
Built to sit outside and be forgotten
The body is 1 mm cold-rolled steel finished in matte black powder coat, with aluminium duct flanges — AC Infinity rate the assembly to withstand inclement weather, which matters because the natural place for an intake filter is at the outside end of the duct run.
Servicing is a hinge-sealed door with a slide lock. Open it, slide the old filter out, slide a new one in, close it. A soft neoprene lining holds the filter square and stops dust creeping around the edges rather than going through the media. There is nothing to dismantle and no ducting to disconnect.
What it filters, and what it does not
The included filter is a pleated particulate filter that traps particles in the 0.3–1.0 micron range — dust, dirt, lint and pollen. That is the right tool for stopping the outside world getting into a subfloor, a roof space, a workshop or a grow room on the intake side.
The chamber accepts any standard 12 × 20 × 1″ (305 × 508 × 25 mm) pleated filter, so you are not locked into one supplier for replacements. Step the MERV rating up if you want finer filtration, bearing in mind that a denser filter costs you more airflow and asks more of the fan.
Where it goes in the run
Fit it at the start of the ductwork, on the intake end, so particles are stopped before they travel through the fan and into the space. Filtering at the far end means the duct and the fan collect everything the filter was meant to catch.
Keep the run as short and straight as you reasonably can either side of the box, and remember that every filter is a restriction. AC Infinity give a minimum airflow range of 80–120 CFM for this size — below that the fan is not moving enough air through the media for the box to be doing much.
Full specifications
| Manufacturer | AC Infinity Inc. |
| Product / model | Air Filter Box 100 mm / AC-AFB4 |
| UPC | 819137021693 |
| Duct diameter | 100 mm (4″) |
| Duct opening size | 97 mm (3.81″) |
| Total dimensions | 596 × 214 × 298 mm |
| Flange length | 82 mm (3.2″) |
| Box material | 1 mm cold-rolled steel |
| Flange material | Aluminium |
| Finish | Matte black powder coat |
| Filter size accepted | 12 × 20 × 1″ (305 × 508 × 25 mm) |
| Included filter | High-efficacy pleated, 0.3–1.0 micron |
| Replacement filters | Any standard MERV filter in the size above |
| Minimum airflow range | 80–120 CFM |
| Maximum airflow | 400 CFM (680 m³/h) |
| Compatible fans | CLOUDLINE S4 and T4 |
| Door | Hinge-sealed with slide lock, neoprene-lined |
| Product manual | Air Filter Box manual (PDF) |
FAQ
Do I need a filter box if I already have a carbon filter?
They are different jobs. A carbon filter scrubs odour from air on its way out. A filter box stops dust, pollen and dirt on the way in. If your problem is smell leaving the space, you want carbon. If your problem is dust, pollen or insects arriving, you want this. Sealed rooms and grow tents pulling fresh air from outside commonly run both.
Will it choke my fan?
It adds resistance — every filter does. That is why AC Infinity recommend pairing it with a high static-pressure mixed-flow fan rather than a cheap axial one. A CLOUDLINE PRO S4 holds airflow under that load where a straight axial fan collapses. If you are close to the limit on airflow, size the fan up rather than skipping the filter.
Where do I get replacement filters in Australia?
The chamber takes a standard 12 × 20 × 1″ (305 × 508 × 25 mm) pleated panel filter — a common HVAC size available from air-conditioning and filtration suppliers. It is a US-standard imperial size rather than a metric one, so search by the inch dimensions. Send us a message if you would rather we pointed you at a supplier.
Can I leave it outside?
It is built for it — steel body, powder coat, aluminium flanges, and AC Infinity rate it for inclement weather. Common sense still applies: get it up off the ground, shelter it from direct driving rain where you can, and make sure water cannot pool at the flange. A soaked pleated filter stops filtering and starts blocking.
How often does the filter need changing?
There is no fixed interval — it depends entirely on how dirty your intake air is and how many hours the fan runs. The practical test is to look at it. When the pleats are visibly grey and loaded, or when you notice airflow has dropped off at the same fan speed, change it. Somewhere the box is easy to reach is worth choosing at install time for exactly this reason.
What size do I need?
Match the fan and the ducting, not the room. This is the 100 mm (4″) box for CLOUDLINE S4 and T4. The others are 150 mm and 200 mm. Reducing a larger fan into a smaller filter box raises static pressure sharply and throws away the airflow you paid for.
Is this genuine AC Infinity stock with an Australian warranty?
Yes. Quick Bloom Lights is the official Australian importer and distributor for AC Infinity. Stock is held in Sydney, orders ship domestically, and the two-year warranty is handled here rather than through an overseas seller.