It may seem slightly premature to approach the subject of greenhouse vents whilst snow is lying on the ground in some parts, but there’s nothing like being prepared! The sun will eventually gain warmth and temperatures will rise – especially under glass.
Even the weak winter sun can have an effect on the temperature inside a greenhouse, and good greenhouse ventilation is as essential as providing heat. Warm air will always rise to the ridge of the greenhouse where it can be dispersed by operating ridge, or roof, mounted vents. This can be done manually or can be made a rather less hazardous task with the introduction of automatic vent openers, which can be set to open the ventilation panels when a certain temperature is reached. A rough guide is to ensure that the roof area that can be opened is equal to 20% of the floor of the structure.
Side ventilation panels are often in the form of adjustable louvre windows, and should be positioned as near to ground level as possible; their function is to replenish the flow of fresh air into the greenhouse and should be as plentiful as is practical. Many greenhouses may contain one or two of these ventilators as standard, but there are kits available which replace a standard pane of glass. The material removed is not wasted as the glass is cut into sections to form the louvre blades. These ventilation panels are much easier to operate by hand but for a fully automated greenhouse – and no worries about overheating when on holiday – automatic openers are also available.