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Rated Excellent on TrustPilot
Order your Greenhouse today with just a 30% deposit
We offer a 10 Year Structural Guarantee

Greenhouse ventilation

Having an effective greenhouse ventilation system is one of the most important things to take into consideration when you are looking to buy a new greenhouse. Read on to learn what steps Cultivar take to create the best greenhouse ventilation designs to ensure the prosperity of your crops.

Our Greenhouse Ventilation Systems

Why Do I Need Greenhouse Ventilation?

Unless you are a cucumber which thrives on high heat and humidity levels, it is essential that your greenhouse is equipped with sufficient ventilation. Plants are like people in so much as they thrive on fresh air. Dense humidity levels and stale stagnant air can often prove fatal to many plants as it can cause them to rot. This is why having a good greenhouse ventilation system is so important if you are to ensure the prosperity of your foliage.

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How much ventilation should your greenhouse have?

As a general guide in the knowledge that hot air rises, we always recommend that the number of vents in the roof of your greenhouse should not be less than 16-20% of the total floor area. So in an 8 by 10 greenhouse, some 12 to 16 square foot should vented. When you buy a Cultivar greenhouse, you will find roof vents on both sides of the ridge which run the full length of the structure at the highest point. This ensures that our greenhouse ventilation systems more than easily exceed 20% of the total floor area. These being frameless offer the maximum light too so you get the best of both worlds. Ridge vents alone will not give your plants the ventilation they need so these should be used in conjunction with low level vents. Ordinary greenhouses have an occasional vent at eaves level but our extraordinary greenhouses have full length aluminium vents at the lowest point. When these open even the smallest amount the cool air is drawn in at the lowest point which is evenly distributed around the greenhouse before being expelled at the ridge through the roof vents.

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Low Level Greenhouse Ventilation

Running along the length of each side at the lowest point you’ll find Cultivar’s unique full length aluminium greenhouse ventilation systems, operated on automatic openers. These in conjunction with the ridge vents provide a superior level of greenhouse ventilation but don’t just take our word for it, here’s the results from an independent assessment.

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Design and Price

The Most Effective Greenhouse Ventilation Systems

The Brief

Cultivar Greenhouses commissioned RPS, a multi-disciplined international group with a detailed understanding of mechanical engineering and fluid dynamics to carry out an assessment on our unique low level vents to ascertain the effectiveness of these as compared to the traditional eaves vents.

To make it more interesting we assumed the model with the eaves ventilation design had the vents running the full length of the greenhouse even though traditional greenhouses usually only rely on occasional vents.

Computational Fluid Dynamics (CFD) simulations combined with dynamic thermal calculations were used to indicate the velocity of air movement and pattern of air movement throughout the greenhouse. A Summer Date of 1st August, based upon the CIBSE Building Energy Code of Manchester, UK, was set for this exercise and a typical glasshouse of measuring 2.4 x 3 metres was used as a model.

The Results

In both instances the internal average peak temperature was some 4 degrees Celsius higher in the greenhouse than the external ambient temperature. There was a minimal difference between the two ventilation systems in the average peak internal temperature. The heat gain was modest as a consequence of high levels of air change. In the case of the Cultivar’s unique plinth level greenhouse ventilation systems, the air change was 34 times in an hour preventing heat build up.

Scientifically proven to have superior air distribution it was proven that cultivar’s unique low level ventilation gives superior distribution of air throughout the greenhouse with no stagnant areas. There was no indication of hot or cold pockets of air with air flowing between 0.2 and 0.4 m/s. The model with the eaves ventilation had a much more uneven flow of air.


In summary, we know how to vent a greenhouse!

Customers should also be aware that they do have the option to have both eaves and low level vents should they have specialist growing requirements for plants such as alpines.

Our Automatic Greenhouse Vents – How They work

The automatic vent openers that come as standard with a Cultivar Greenhouse are a simple wax filled cylinder mechanism that expands when warm, pushes out a piston which in turn forces the vents open, no electric is required. This means if you’re not there on a warm day your plants will get the ventilation they need.

Optionally manual openers can be added at eaves level

What else should be considered?

Whilst continuous humid conditions are not desirable in excessive summer heat dry conditions can be harmful too. Obviously frequent watering is essential but ‘damping down’ by spraying the floor and benches with water will help provide good levels of humidity. If you are unable to offer your greenhouse fairly constant attention perhaps an automated watering system should be considered.

Heat build can be corrected with automatic openers or by opening your vents, some plants such as alpines require constant extensive greenhouse ventilation and in this instance we can provide additional ventilation. On the glass to ground and panelled models there are, as standard, low level vents but extra manual vents can be added too just below the eaves.

The even circulation of air through the low level and roof vents is rewarded with healthy plants. Opening the door will help in the more extreme cases, although hot summer days don’t seem to last. Enthusiasts might also consider a re-circulating fan which may double up as a greenhouse heater for winter use. This will provide your plants with air movement, a popular method used by commercial growers for guaranteed result.

If you have specialist growing needs then feel free to talk to us about the most suitable greenhouse ventilation designs prior to making your decision. In the instance that you would like two different growing environments then a partition can be added so you can keep your cucumbers happy in one section without affecting the plants in the rest of the greenhouse.

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