Growing guide
CO₂ in grow rooms: enrichment basics and why you should check your sensors
Adding CO₂ only pays off when the light is strong enough, the gas reaches the leaves and the sensor tells the truth. Target levels, safety limits and what our own sensor data taught us.
Outdoor air contains about 420 ppm of CO₂. Under strong light, plants can use more than that, so sealed grow rooms often add CO₂ to speed up photosynthesis. It is one of the most effective upgrades a high-light room can make — and one of the easiest to waste.
When enrichment helps
- Only with enough light. Below roughly 600 µmol/m²/s, light is the limit and extra CO₂ does little. Read our guide to PPFD and DLI first.
- Only while the lights are on. Plants do not use CO₂ for photosynthesis in the dark.
- Only in a room you can keep closed. If the exhaust fan runs constantly, the CO₂ goes straight outside.
Target levels
| Situation | CO₂ (ppm) |
|---|---|
| Outdoor air | ≈ 420 |
| Seedlings, clones, low light | Ambient to 800 |
| Vegetative growth under strong light | 800–1,200 |
| Flowering under strong light | 1,000–1,500 |
| Benefit levels off | Above ≈ 1,500 |
What our sensor data showed
We analysed the history of 14 sensors across four rooms on a farm we work with. In rooms with good air mixing, CO₂ readings should agree within a small margin. Instead, two sensors in the same room differed by up to 430 ppm at the same moment.
- One sensor regularly read below outdoor air — around 340 ppm, which is not possible in a room that is being enriched.
- Another drifted upwards day after day, from about 175 ppm above the room average to more than 470 ppm above it in ten days.
- A third collapsed within five days and had to be replaced.
That gap is the difference between "enriched" and "barely above outdoor air". A controller that doses CO₂ from a drifting sensor will over- or under-dose without anyone noticing. Sensors age, and a single sensor gives you no way to tell.
Placement, mixing and checks
- Mount the CO₂ sensor at canopy height, in the middle of the growing area — not next to the CO₂ outlet, a door or an exhaust fan.
- In large rooms, use more than one sensor and compare them. If one keeps moving away from the others, check or replace it.
- Sanity-check against outdoor air: with enrichment off and the room ventilated, a sensor should read close to 420 ppm.
- Keep air moving under and through the canopy so the gas reaches the lower leaves.
- Release CO₂ above the canopy: it is heavier than air and sinks as it mixes.
In Big G rooms, EC160 duct fans feed the wind-tunnel system that pushes air through the canopy, and G_Control reads CO₂, temperature and humidity from its tri-sensor so dosing and ventilation work from the same numbers.
Planning a room?
Send us the room size and the crop. Our engineers will suggest a lighting and control layout that fits.
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