Your inline fan removes heat and humidity and brings in fresh air. Your carbon filter keeps odour inside. Matched, both work. Mismatched, you pay more for a worse result.
A bigger fan can make smell worse
Carbon only traps odour if air stays in it for 0.1 to 0.15 seconds. Push more air through the same filter and odour rushes straight past. Before you buy a bigger fan, check the fan-to-filter seal, the tent humidity and the age of the carbon.
How to size it
- Work out tent volume in cubic feet, aim for 1 air change a minute, then add 25% for the filter and 20% for ducting.
- A 1.2 x 1.2 x 2.0m tent is about 102 cubic feet, so you need about 153 CFM. A 100mm fan covers it.
- Choose a filter rated at or above the fan's airflow, and run the fan on a speed controller.
- Extract slightly more than comes in, so all air leaves through the filter.
| Duct size | Fan (rated airflow) | Matching filter (rated capacity) |
|---|---|---|
| 100mm | Headwind HVC EC 100mm: 275 m³/h, 160 CFM | Headwind HVC 100 x 300mm: 340 m³/h, 200 CFM |
| 125mm | Headwind HVC EC 125mm: 280 m³/h, 166 CFM | Headwind HVC 125 x 300mm: 408 m³/h, 240 CFM |
| 150mm | Headwind HVC Silenced 150mm: 594 m³/h, 350 CFM | Headwind HVC 150 x 300mm: 595 m³/h, 350 CFM |
| 200mm | Headwind HVC Silenced 200mm: 1,205 m³/h, 710 CFM | Headwind HVC 200 x 750mm: 1,360 m³/h, 800 CFM |
| 250mm | Headwind HVC Silenced 250mm: 1,808 m³/h, 1,065 CFM | Headwind HVC 250 x 1000mm: 2,380 m³/h, 1,400 CFM |
Running 315mm? Can-Lite 2500 and 3000 have a 315mm flange. See all fans and Can-Filters, and seal joints with clamps and duct tape.
Fan and filter questions
What size inline fan do I need for my tent?
Tent volume in cubic feet, times 1.5 to allow for the filter and ducting, gives the CFM for 1 air change a minute. A 1.2 x 1.2m tent needs about 153 CFM, so 100 or 125mm. A 1.5m tent suits 150mm. A 2.4 x 2.4m tent suits 200mm.
Why does my carbon filter still smell?
Usually 1 of 4 things: a leaky seal between fan and filter, high humidity filling the carbon with water, a fan pushing air through faster than the carbon can catch it, or a filter at the end of its life. Bigger fans make the third one worse.
How long does a carbon filter last?
Typically 12 to 24 months of continuous use, longer for deep carbon beds. Can-Filters rate the Can-Lite at a minimum of 18 months. Heat, humidity and dust shorten it, so control humidity and wash the pre-filter.
Do I need a fan speed controller?
Yes. It is the cheapest climate upgrade there is. It lets 1 fan run hard in summer and gently in winter, and it keeps airflow at or under your filter's rating. Many EC fans, including the Headwind HVC range, come with one.
