# Carbon filter

> A carbon filter scrubs odour from exhaust air by passing it through activated carbon, which adsorbs aroma compounds such as terpenes.

- Canonical: https://genetixbay.com/knowledge/glossary/carbon-filter.html
- Also written: charcoal filter, activated carbon filter, odour filter, odor filter, scrubber, can filter
- Glossary category: Environment and light · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

A carbon filter is a cylinder or panel packed with activated carbon, mounted on the [exhaust](https://genetixbay.com/knowledge/glossary/exhaust-fan.md) line so all air leaving the grow space passes through it. Activated carbon has an enormous internal surface area that adsorbs volatile organic compounds, including the [terpenes](https://genetixbay.com/knowledge/glossary/terpene.md) and [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md) compounds that make cannabis smell. It does not remove humidity or heat.

## In practice

Typical setup: filter in the tent, fan pulling air through the filter, then ducting outside. Match the filter's rated airflow to the fan's real [CFM](https://genetixbay.com/knowledge/glossary/cfm.md). Bed depth matters; deeper carbon beds give air more contact time and last longer.

Filters saturate over time. Lifespan is roughly 12–24 months in normal use. High humidity, above about 70% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md), shortens it because water occupies adsorption sites, and dust clogs it, so keep the pre-filter sleeve clean and replace it when grey. When odour starts leaking with [negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md) confirmed, the carbon is spent.

Some growers lose aroma control in late flower when terpene output peaks. Lower fan speed slightly to increase contact time rather than running full blast.

## Don't confuse with

- **Ozone generators**: oxidise odours; harmful to people and plants at effective concentrations.
- **HEPA filter**: removes particles, not odour.

## Related terms

[Exhaust fan](https://genetixbay.com/knowledge/glossary/exhaust-fan.md), [Negative pressure](https://genetixbay.com/knowledge/glossary/negative-pressure.md), [CFM](https://genetixbay.com/knowledge/glossary/cfm.md), [Relative humidity](https://genetixbay.com/knowledge/glossary/relative-humidity.md)

## Read more

- [Airflow: air exchange, canopy air speed and fan placement](https://genetixbay.com/knowledge/environment/airflow.md)