How long does a 20lb CO2 tank last in a 4x4 tent?
Short answer: about 14–28 days running 12 hours a day, depending on how leaky your tent is.
Watch the full setup
Prefer to see it built? Here's the full AC Infinity CO2 automation walkthrough.
More AC Infinity gear reviewsA 20lb CO2 tank holds roughly 9.07 kg of CO2, which works out to about 4,945 liters of gas at standard conditions. That sounds like a lot, and it is, but a sealed grow tent is rarely fully sealed.
Assumptions
| Tent volume (4x4x7) | 112 ft³ |
| Target ambient CO2 | 400 ppm |
| Enrichment target | 1,200 ppm |
| Photoperiod | 12 hours |
| Air leak rate (typical sealed tent) | ~1 air change/hr |
The math
To raise the tent from 400 → 1,200 ppm requires injecting roughly 2.5 ft³of CO2 into a 4x4x7 tent. Over a 12-hour photoperiod with a typical 1 air-change-per-hour leak rate, you'll need to top up about 10–12 times per cycle. Call it 30 ft³ per day.
A 20lb tank is roughly 175 ft³ of usable CO2. Divide that by ~30 ft³/day and you land near the 6-day mark if your tent leaks fast. A well-sealed tent with good HVAC sealing can stretch that to 3–4 weeks.
What actually changes the answer
- Tent seal quality: duct boots, zipper integrity, exhaust dampers.
- Whether your inline fan runs during enrichment. If yes, you're venting CO2 straight out.
- Plant uptake: late veg / early flower plants in dense canopy use more.
- Target ppm: 800 vs 1,200 vs 1,500 ppm massively changes consumption.
- Regulator + controller accuracy: cheap solenoids overshoot.
My setup
I run a 4x4 tent with the AC Infinity Controller AI+ managing CO2 dosing on top of temp, humidity, and exhaust. Sealed reasonably well, exhaust shuts off during dosing, target 1,200 ppm. I typically refill every 2½ months on a 20lb tank.
Numbers are rounded for readability. Your mileage will vary. Measure with a real CO2 sensor, not assumptions.