Greenhouse Ventilation is achieved with a combination of roof vents, louvre vents, greenhouse door and fans. Excellent ventilation is essential if your greenhouse crops are to thrive. Greenhouse Ventilation controls both the temperature and humidity of the air in the greenhouse - both of which are essential factors when it comes to healthy plant growth and bumper crops. Basically you need cool air to be drawn into the greenhouse and hot air to be driven out. This can be achieved by the installation of sufficient vents - such as louvre vents and roof vents - ideally fitted with automatic openers, together with the use of greenhouse fans. If you intend to grow in your greenhouse all year round then consider fitting an extractor fan in the greenhouse. Extractor fans are designed to completely replace the air in a greenhouse every few minutes even on the hottest days. Attached to a thermostat, the fan will run automatically. Remember that it is always better to over ventilate your greenhouse than under ventilate it.