Example data table
| Space (m³) | Current (ppm) | Target (ppm) | ACH | Boost (g) | Flow (L/min) | Maintenance (g/h) |
|---|---|---|---|---|---|---|
| 43.2 | 420 | 1000 | 0.5 | 1,250 | 7.7 | ~410 |
| 100.0 | 450 | 1200 | 1.0 | 3,200 | 10.5 | ~1,600 |
| 20.0 | 420 | 900 | 0.2 | 330 | 2.2 | ~90 |
Formula used
- Room moles (ideal gas): n = (P·V)/(R·T)
- CO2 boost moles: n_CO2 = (Δppm/1,000,000) · n
- CO2 boost mass: m(g) = n_CO2 · 44.01
- CO2 gas volume at room conditions: V_CO2 = n_CO2·R·T/P
- Ventilation maintenance (steady-state): g/h ≈ ACH·(Target−Ambient)·(n/1e6)·44.01
How to use this calculator
- Pick your unit system and volume method.
- Enter space size, temperature, and pressure.
- Set current, target, and ambient CO2 ppm.
- Choose how fast you want to reach target ppm.
- Enter ventilation as ACH or fan flow in CFM.
- Optionally include plant uptake for tighter planning.
- Set your schedule and source details to estimate cost.
- Measure ppm where plants breathe, not at the ceiling.
- Enrich only during lights-on for most crops.
- Reduce ventilation during enrichment if safe and permitted.
- Always use a CO2 monitor and follow safety guidance.
Crop targets and response
Most indoor gardens enrich between 800–1,200 ppm during lights-on. Seedlings and stressed plants often perform best at the low end, while fast-growing fruiting crops can benefit nearer the upper end when light, temperature, and nutrition are already optimized. If light is low or temperatures are cool, raising CO₂ alone may not help. Above ~1,500 ppm, returns often diminish and control risk rises.
Ventilation drives the maintenance dose
Every air change replaces enriched air with ambient air. Maintenance demand scales with (target − ambient) and the air exchange rate (ACH). At 0.5 ACH, the required steady injection is roughly half of what it would be at 1.0 ACH for the same volume and ppm setpoints. Treat “leakage” as hidden ACH from doors, duct backflow, and negative pressure.
Ramp time and mixing quality
The boost dose is the one-time mass needed to move from current ppm to target ppm. Your chosen enrichment time converts that mass into a flow rate. Short ramp times increase required flow and can overshoot if mixing is uneven, so use circulation fans and place sensors at canopy height. A slightly longer ramp can improve stability and reduce waste.
Source sizing and weekly planning
Once you know boost grams and maintenance grams per hour, multiply by lights-on hours and grow days to estimate weekly consumption. Cylinder systems are easy to size by flow and purity, and the calculator can estimate cost per kilogram delivered. Generators add heat and water vapor, so account for HVAC load and ventilation strategy.
Example data you can compare
Scenario: 30 m³ room (4×3×2.5 m), 25°C, 101.3 kPa, 450→1,200 ppm, ambient 420 ppm, 10‑minute ramp, 0.7 ACH, canopy 8 m², uptake 1.0 g/m²/h, 12 h/day, 6 days/week.
| Metric | Value | Unit |
|---|---|---|
| One-time boost | 40.5 | g CO₂ |
| Flow to reach target | 2.25 | L/min |
| Maintenance at target | 37.5 | g/h |
| Estimated weekly total | 2.94 | kg CO₂ |
FAQs
1) What target ppm should I use for leafy greens?
A common range is 800–1,000 ppm during lights-on. Start lower if light intensity or temperature is modest, and increase only after monitoring plant response, transpiration, and nutrient uptake.
2) Why does high ventilation make CO₂ expensive?
Ventilation replaces enriched air with ambient air. Higher ACH increases the dilution rate, so you must inject more CO₂ each hour to hold the same target ppm.
3) Should I enrich when lights are off?
Usually no. Photosynthesis is minimal in darkness, so enrichment is wasted and can raise safety risk. Most growers enrich only during the photoperiod.
4) How do I estimate ACH if I only know fan CFM?
Convert CFM to m³/h, then divide by room volume to get ACH. The calculator can do this when you switch ventilation mode to CFM.
5) Do plants consume CO₂ fast enough to matter?
It depends on canopy size, light, and growth rate. In dense, well-lit canopies, uptake can be meaningful, so adding a g/m²/h estimate helps prevent under-dosing.
6) Can CO₂ enrichment harm plants?
Yes, if it causes heat stress, poor VPD control, or inconsistent spikes. Maintain stable temperature, humidity, and airflow, and avoid pushing ppm far beyond your crop’s effective range.
7) What safety steps are essential?
Use a calibrated CO₂ monitor with alarms, keep cylinders secured, verify ventilation control, and follow local regulations. Never work in a sealed room with elevated CO₂ without proper monitoring.