How long does a 20lb CO2 tank last in a 4x4 tent?
Honest answer: there is no single number. The tank holds a lot of gas, so tank life comes down to how fast enriched air leaks out. Realistically, a few weeks to a couple of months at 1,200 ppm running 12 hours a day. My own well-sealed tent lasts about 2½ months.
Reviewed
Watch the full setup
Prefer to see it built? Here's the full AC Infinity CO2 automation walkthrough.
More AC Infinity gear reviewsA 20lb tank holds 9.07 kg of CO2. At room temperature (about 68°F / 20°C) that is roughly 4,950 liters of gas, or about 175 ft³. That is a large amount, and it is the reason the answer is not a small number of days.
Inputs
| Tent volume (4x4x7) | 112 ft³ (≈ 3,170 L) |
| Tank contents (20 lb / 9.07 kg CO2) | ≈ 4,950 L at 68°F |
| Target ambient CO2 | 400 ppm |
| Enrichment target | 1,200 ppm |
| Photoperiod | 12 hours |
The math, in one consistent unit
Work it in liters so the units stay honest. Raising a 112 ft³ tent from 400 to 1,200 ppm is a change of 800 ppm, which is 0.08% of the tent volume:
112 ft³ × 0.0008 ≈ 0.09 ft³ ≈ 2.5 liters of CO2 per re-enrichment
The tank holds about 4,950 liters. That is roughly 1,900 full re-enrichments worth of gas. So the tank capacity is not the limiting factor. What sets tank life is how often you have to re-dose, and that is driven almost entirely by how fast enriched air escapes the tent through leaks and the exhaust, plus what the plants take up.
A note on units: an earlier version of this page reported the per-fill volume and daily use in cubic feet when the figures were actually in liters, which produced a misleadingly short estimate. The numbers above are corrected and kept in liters throughout.
Realistic ranges by setup
| Setup | What drives it | Est. tank life |
|---|---|---|
| Well sealed, exhaust off during dosing | Only plant uptake and slow leakage consume CO2. | ~2 to 3 months |
| Typical hobby tent | Moderate infiltration, some exhaust overlap, solenoid overshoot. | ~3 to 6 weeks |
| Leaky, or exhaust runs during dosing | Enriched air is vented about as fast as it's injected. | Days to ~2 weeks, and mostly wasted |
These are estimates for a 4x4 running 12 hours a day at 1,200 ppm, not measured per-setup figures. Treat them as a starting point and confirm with a real CO2 sensor.
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 changes consumption a lot.
- Regulator + controller accuracy: a wide dead band and solenoid overshoot waste gas.
My setup (one data point)
I run a 4x4 tent with the AC Infinity Controller AI+ managing CO2 dosing alongside temp, humidity, and exhaust. Sealed reasonably well, exhaust shuts off during dosing, target 1,200 ppm. On that setup I refill about every 2½ monthson a 20lb tank. That is one tent's result at the well-sealed end of the range above, not a number you should expect to hit in a different setup.
Safety with compressed CO2
- Secure the tank upright with a chain or strap so it cannot fall. A knocked-over tank can shear its valve.
- Use a regulator rated for CO2, and follow the equipment's instructions.
- CO2 is heavier than air and displaces oxygen. Enrich an unoccupied space and ventilate before you spend time in the room.
- Do not enrich a room while people or pets are inside it.
- A CO2 monitor with an alarm is worth having if you enrich indoors.
Sources: gas volume from the ideal-gas molar volume of CO2 (44.01 g/mol) at 68°F. Tank life ranges are estimates; measure your own with a real CO2 sensor. Reviewed .