Ventilation is the most important climate tool in a greenhouse — it dumps excess heat, moves humid air out and keeps air circulating to prevent disease. This page covers the kit: vents, automatic openers and fans, and how to choose them.
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Automatic vent openers
Non-electric automatic vent openers use a wax cylinder that expands with heat to push a roof vent open, then closes as it cools. Inexpensive and invaluable — they vent while you’re out and prevent the classic sunny-day overheating disaster.
Circulation vs extraction fans
- Circulation fans keep air moving even when vents are shut — vital in cool, still, humid spells to prevent botrytis“>botrytis and downy mildew“>downy mildew.
- Extraction fans actively pull hot air out for cooling in hot climates, often paired with an intake louvre.
Greenhouse fans
Automatic vent openers
How to choose
Maximise vent area first (add a louvre if under-vented), fit an automatic opener, then add a circulation fan for airflow and an extraction fan if you struggle with summer heat. The how-to is in the greenhouse ventilation“>greenhouse ventilation guide; for hot climates see how to cool a greenhouse.
Related guides
- Climate control“>Climate control · shade cloth“>shade cloth · ventilation guide“>ventilation guide · greenhouses hub“>greenhouses hub