How much ventilation do I need?
Ventilation is so important in a greenhouse. Air movement will lower temps, remove hot or cold spots and help create micro climates for your plants. Winter time ventilation helps to heat the greenhouse evenly, while summertime ventilation will help remove hot spots, keep plants dry and help with cooling if using misting or fogging systems. Running fans is a great way to control bacteria and fungus from collecting on wet leaves.
One of the simplest and best ways to ventilate your greenhouse is to provide natural air flow across your greenhouse at a high level and a low level if possible. This can be accomplished with windows, doors, vents, or fans. If you are using a plastic covering on your greenhouse you can remove a portion or gather it up to provide side ventilation.
Fans can be as inexpensive as a box fan purchased at a super store or a specialty exhaust fan.
A couple of tips are to place your fan high for more efficient cooling and position it to pull the air across the length of the greenhouse and then exhaust it to the outside.
When you are installing vents in your greenhouse, remember to provide a way to seal them for the winter!