CO₂ enrichment
How much CO₂ it takes to fill a room to a setpoint and hold it there through the light period.
Room & targets
Length × width × height
Leakage; sealed rooms 0.1–0.5
CO₂ needed
Per day
0.21kg
Initial fill
16.4L
Leakage
8.2L/h
Tank lasts
43.1days
How this is calculated
Fill (sealed room)
CO₂ volume = room volume × (target − ambient) / 10⁶ (sealed room, no leakage)
Holding the setpoint
fill = V × (target − ambient)/10⁶; leakage/h = V × air changes/h × (target − ambient)/10⁶; daily = fill + leakage × lights-on hours; kg = L × 1.83 g/L
- Leakage rate is the biggest unknown: measure it by watching how fast ppm falls with the CO₂ off.
- Enrich only while lights are on; plants do not use CO₂ in the dark.
Cited targets
From the genetics.guru grow library, in the units each source used. Grades: strong and moderate are peer-reviewed; community practice is untested.
CO2 (ambient baseline, measured in unenriched trial rooms)any400–480 ppmModerate
Measure your own room; Guelph trials 437 (day) / 479 (night) ppm.
2 sources
- Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
- Ahrens A, Llewellyn D, Zheng Y (2024-02-01). Longer Photoperiod Substantially Increases Indoor-Grown Cannabis’ Yield and Quality: A Study of Two High-THC Cultivars Grown under 12 h vs. 13 h Days — Plants 13(3):433
CO2 enrichment setpoint (lights on)vegetative and flower800–1,200 ppmModerate
~40% yield at 1200 ppm (dissertation); leaf photosynthesis +38-50% at 700-750 ppm. No cannabis evidence of further gains above ~1200-1500 ppm. Only in sealed/low-exchange rooms.
5 sources
- Westmoreland FM (chair: Bugbee B) (2024). Environmental physiology of medical cannabis (PhD dissertation, Utah State University)
- Chandra S, Lata H, Khan IA, Elsohly MA (2008-10). Photosynthetic response of Cannabis sativa L. to variations in photosynthetic photon flux densities, temperature and CO2 conditions — Physiology and Molecular Biology of Plants 14(4):299-306
- Chandra S, Lata H, Khan IA, ElSohly MA (2011-07). Photosynthetic response of Cannabis sativa L., an important medicinal plant, to elevated levels of CO2 — Physiology and Molecular Biology of Plants 17(3):291-295
- Westmoreland FM, Kusuma P, Bugbee B (2021-03-23). Cannabis lighting: Decreasing blue photon fraction increases yield but efficacy is more important for cost effective production of cannabinoids — PLOS ONE 16(3):e0248988
- Kimball BA (1983-09). Carbon Dioxide and Agricultural Yield: An Assemblage and Analysis of 430 Prior Observations1 — Agronomy Journal 75(5):779-788
PPFD at which CO2 enrichment pays offflowerNot establishedCommunity practice
Not established for cannabis. High light paid off at ambient CO2 up to 1800 umol. 1:1 ppm:PPFD is a vendor/forum rule. Calculator should compute economics, not enforce a threshold.
2 sources
- Rodriguez-Morrison V, Llewellyn D, Zheng Y (2021-05-11). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment — Frontiers in Plant Science 12:646020
- THCFarmer thread 'What PAR are you cooking under ??' (Growtime818, Dirtbag, ImpulsiveGrower et al.) (2021-08-23). Growers running 950–1500 PPFD with 1000–1600 ppm CO2
CO2 exposure limit (8-h TWA, NIOSH REL / OSHA PEL)any≤ 5,000 ppmStrong
Short-term limit 30,000 ppm; IDLH 40,000 ppm. Require a monitor/alarm.
1 source