CO₂ calculator

Formula — CO₂ calculator

CO₂ demand has two parts — the one-off charge that lifts the room from ambient to target, and a continuous make-up flow that replaces what leaks out. Density comes from the ideal gas law rather than a fixed constant, because it drops from 1.83 kg/m³ at 20 °C to 1.80 kg/m³ at 25 °C.

• density [kg/m³] = (101325 × 0.04401) ÷ (8.314 × (T + 273.15))
• Δppm = target − ambient
• pure CO₂ volume [m³] = room volume × Δppm × 10⁻⁶
• mass per fill [g] = CO₂ volume × density × 1000
• make-up [g/h] = mass per fill × leakage ACH
• per day [g] = mass per fill + make-up × dosing hours
• propane [kg] = CO₂ [kg] ÷ 3.0 (and 46.3 MJ of heat per kg burned)

• Leakage ACH by build: sealed 0.25, tight 0.5, average 1.0, leaky 2.0.
• Practical plant ceiling 1500 ppm; the 8-hour human exposure limit is 5000 ppm.

Worked example — CO₂ calculator

A 120 × 120 × 200 cm room holds 2.88 m³. Lifting it from 420 ppm to 1200 ppm is a Δ of 780 ppm, which is 2.88 × 780 × 10⁻⁶ = 0.00225 m³ of pure CO₂. At 25 °C (1.80 kg/m³) that is about 4.0 g per fill — a trivial amount, which is why the running loss dominates.

With an average-tightness room (1.0 ACH) the make-up demand is also ≈4.0 g/h. Dosing for 12 h a day costs 4.0 + 4.0 × 12 ≈ 52 g/day, or about 4.7 kg over a 90-day run. A 10 kg bottle therefore lasts roughly 190 days of dosing — two full grows. Sealing the same room to 0.5 ACH halves the make-up and takes the season down to about 2.5 kg. Generating that CO₂ by burning propane instead would need ≈1.6 kg of gas and release about 73 MJ of extra heat, which is why burners belong in cold rooms with real cooling capacity.

Typical ranges — CO₂ calculator

Enrichment only pays off when light, temperature and nutrition are already at the top of their bands. Below about 600 PPFD, extra CO₂ changes almost nothing; above 1000 PPFD it is often the limiting factor. Never dose a room people work in without ventilation interlocks and a monitor.