Storage CO₂ & Know When to Vent
Protects apples
Respiring produce fills a sealed store with carbon dioxide — enter the store volume, produce weight and respiration rate to get the hours until the CO₂ ceiling and the ventilation rate to hold it.
Describe the store
Next: set the exhaust fan to at least 0.3 m³/h of fresh-air exchange, or open vents before 131 h elapse, to keep CO₂ under 5%.
High CO₂ causes off-flavours and internal browning in many crops. Respiration roughly doubles every 10°C, so colder stores buy you more time between vent cycles.
Storage CO₂ — key facts
- Source of CO₂
- produce respiration
- Hours to vent
- CO₂ rise × air volume ÷ output
- Vent rate
- airflow to hold the ceiling
- Faster build-up
- warm or active crops
- Risk
- produce injury, unsafe entry
- Atmosphere CO₂
- ≈ 0.04% start
- Measure with
- CO₂ meter in store
- Privacy
- Runs in your browser; nothing uploaded
Sealed produce keeps breathing — and the air fills up
Harvested produce is still alive: it breathes in oxygen and breathes out carbon dioxide. Shut it in a sealed store and that CO₂ has nowhere to go, so the concentration climbs until it harms the crop or makes the room unsafe to enter. How fast depends on how much produce there is, how actively it respires and how much air space surrounds it — which is exactly the balance this calculator runs to tell you when to open the vents.
This tool gives the hours to vent, the ventilation rate, the CO₂ per hour and the store from the store volume, produce weight and respiration rate. Use it to set a venting schedule, size a fan and keep both produce and people safe. Pair it with the Equilibrium Moisture Content and Cold Chain Breach tools for a full storage plan.
Vent in time
Know the hours before CO₂ hits the ceiling.
Size the fan
Get the airflow that holds CO₂ steady.
Protect the crop
Keep CO₂ below the level that injures produce.
Keep entry safe
Stay under occupational CO₂ limits for workers.
Frequently Asked Questions
How are the hours to vent calculated?+
From the CO₂ the produce makes and the air space it fills. Total CO₂ output = produce weight × respiration rate. The store starts near atmospheric CO₂ (~0.04%) and the headspace of air can only hold so much before reaching your set ceiling. Hours to vent = (allowable CO₂ rise × store air volume) ÷ (CO₂ output per hour). The calculator does this in one step.
Why does CO₂ build up in a sealed store?+
Harvested fruit, vegetables and grain are still alive and respiring — they take in oxygen and breathe out carbon dioxide. In a sealed room with no airflow, that CO₂ has nowhere to go, so its concentration climbs steadily. Warmer produce and more active crops respire faster, filling the store sooner, which is why ventilation timing matters.
What CO₂ level is too high?+
It depends on the crop and on safety limits. Many fresh products tolerate only a few percent CO₂ before suffering injury, off-flavours or decay, while workers must not enter air above the occupational CO₂ limit. Setting a sensible ceiling — often well below a few percent for produce, and below safe-entry limits for people — tells the calculator when the store must be vented.
What does the ventilation rate output mean?+
It is the steady airflow, in cubic metres per hour, needed to carry CO₂ out as fast as the produce makes it, holding the concentration at your ceiling instead of letting it climb. Run a fan at or above that rate and the store stays in balance; below it, CO₂ slowly accumulates and you fall back on the hours-to-vent figure.
How is respiration rate expressed?+
Usually as CO₂ produced per unit weight per hour — for example millilitres or milligrams of CO₂ per kilogram per hour. It rises sharply with temperature and varies by crop: leafy greens and broccoli respire fast, while potatoes and apples are slow. Using a value for your crop at its storage temperature makes the CO₂ and ventilation figures realistic.
Why does temperature change the answer so much?+
Respiration roughly doubles or more for every 10°C rise, so warm produce pours out CO₂ far faster than chilled produce. That means a warm store hits the ceiling in a fraction of the time and needs much more ventilation. Cooling the store both slows respiration and stretches the time between vents — one reason cold storage and ventilation go together.
Does this assume the store is airtight?+
The hours-to-vent figure assumes a sealed space with no leakage, which is the conservative case — it tells you the soonest you'd reach the ceiling. Real stores leak a little, so in practice you have at least that long. Use the figure to set a safe venting schedule and the ventilation rate to size a fan for continuous control.
Does this work for any store and crop?+
Yes — a small cold room or a large bulk store, apples, potatoes, onions, grain or leafy crops all follow the same balance of CO₂ produced versus air volume. Enter the store volume, produce weight and respiration rate; only those numbers change between cases, the calculation is the same.
Are the figures precise?+
They're solid planning figures. Respiration rates vary with crop, variety, temperature and ripeness, and real stores leak and stratify, so confirm with a CO₂ meter in the room. Use the hours-to-vent and ventilation-rate outputs to set a safe schedule and fan size, then verify against actual readings.