Wind ventilation system. The position of ventilators is important in the air exchange in the greenhouse. If ventilators are placed on the sides and roof of the greenhouse and are also staggered, this will ensure that air circulates throughout the entire area of the greenhouse. If vents are placed directly opposite one another, air will simply blow straight through the greenhouse. To increase ventilation over the summer you may also keep the doors open.
Chimney ventilation system. This system depends on warm, humid air rising out of roof vents and being replaced by fresh air that is drawn in as a result through lower ventilations, which are usually positioned along the sides of the greenhouse either above or below the staging.
Fan ventilation system. This is a mechanically driven system that works by extracting air from the greenhouse at head height or slightly higher and drawing in fresh air through vents lower down and usually at the opposite end of the greenhouse.
Hinged ventilators. This system will allow maximum airflow while at the same time will prevent direct gusts of wind from entering the greenhouse. These may be fitted to the sides or roof of the greenhouse and should open wide to an angle of about 45 degrees.
Louvre ventilators. This system is particularly useful for controlling the airflow throughout the greenhouse in winter, when the roof ventilators may allow too much heat to escape. Louvre vents are usually positioned below the height of the staging and must close tightly so that they exclude all draughts.
Automatic vent openers. This system simplifies the temperature control in the greenhouse as they open automatically. They should be fitted to at least some of the hinged or louvre ventilators. There are many models of autovent openers available. Chose the ones that suit you best.
Extractor fans. Primarily designed to be used in the kitchen, this system is also ideally suited for use in the greenhouse. Choose a fan that is powerful enough for the particular size of your greenhouse. A louvre window positioned at the opposite end of the greenhouse to the extractor fan and set lower down is essential to provide a flow of fresh air to replace the stale air that is drawn out by the fan.