Ventilation for growing cannabis indoors

Growing cannabis indoors requires special attention to ventilation. Unlike outdoor environments where natural airflow disperses heat and humidity, indoor cultivation needs artificial air circulation to maintain optimal humidity, temperature, and CO₂ levels.

Importance of ventilation for cannabis cultivation

Exhaust systems remove hot air, while fresh air is introduced from outside or through air conditioning. Fans are essential to distribute airflow evenly, prevent stagnant zones, and mimic outdoor conditions.

Daytime ventilation

When lights are on, cannabis releases more heat and moisture. Use an exhaust system to avoid overheating and excess humidity. Hot air rises, so place fans to evenly circulate air and prevent heat build-up at the top of the room.

Note: do not point fans directly at plants as it can cause stress and reduce yields. Instead, use several low-power fans directed under the lights.

Nighttime ventilation

When lights are off, humidity increases, which can lead to mold and fungus, especially botrytis. Run fans periodically (15–30 minutes every hour). Early in growth, night ventilation is less critical due to limited foliage.

Exhaust system and power calculation

An exhaust system is essential for fresh CO₂-rich air, reducing heat and humidity, and controlling odor via a carbon filter. Without it, cannabis smells may spread beyond the grow room.

To calculate the required exhaust power:

• Room volume (length × width × height)
• Air exchange per hour (volume × 60)
• Adjust for humidity/temperature (×2 for winter, ×3 for year-round)

Example: 1 × 1 × 2 m = 2 m³; required power = 2 × 60 × 3 = 360 m³/h

Night ventilation and humidity control

Keep humidity below 60% during flowering. If exhaust isn’t enough, use a dehumidifier. Install extra carbon filters to prevent odor leaks at night.

Air intake system

Air intake can be passive (vents, gaps) or active (fans). With fans, intake should be half the strength of the exhaust and equipped with insect filters.

General ventilation tips

• Seal all connections tightly to prevent odor leaks.
• Do pre-calculations before buying equipment.
• Use high-quality filters to ensure discretion.

Properly configured ventilation for growing cannabis seeds ensures healthy cannabis growth, a good harvest, and no problems with fungi or odors.

Important!!! Sunny Seeds does not provide assistance in growing cannabis. We remind you that such activities are contrary to Ukrainian law. This publication is intended solely for informational and scientific purposes.