Why does a greenhouse need a vent?

Written by edith hignutt
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Why does a greenhouse need a vent?
A greenhouse door can assist proper venting. (Metal greenhouse in summer with open door image by Scott Latham from Fotolia.com)

A greenhouse without any vents can have the same effect as a magnifying glass in the sunlight on your plants. Simply opening the door or a window in the greenhouse is not enough for prosperous plants. Vents do more than let heat escape. Proper venting allows for optimum climate control allowing you to use your greenhouse all year long.

Temperature Control

The sun shining on the greenhouse exterior is amplified to warm the interior. While this effect keeps the greenhouse warm during cooler daytime weather and nights, it can damage plants during sunny hot days. Vents allow the hotter air to escape and cooler outside air to enter. By carefully monitoring the greenhouse temperature, vents can be adjusted to keep the plants within their comfort zones.

Gas Exchange

Plants "breathe" carbon dioxide and "exhale" oxygen. Vents allow the gases to freely exchange, refreshing the level of carbon dioxide inside the greenhouse. Without this air exchange, plants can suffocate.

Humidity Control

In winter months the cold air on the exterior causes condensation to build up on the interior. While some humidity is a necessity in a greenhouse, too much can lead to disease and unhealthy plants. Roof vents are particularly adept at reducing humidity without allowing an excess of cold air inside.

Air Circulation

The placement of vents control and direct air flow in the greenhouse. Without considering circulation, greenhouses can have hot and cool areas along with the respective change in humidity. Good ventilation evens out the interior temperature and humidity levels.

Vents should be placed diagonally across the greenhouse, with one up high and one down low. Roof vents provide excellent ventilation but need to be supplemented with side vents. Opening up the greenhouse door serves as ventilation when outdoor temperatures are within a safe range for the plants.

The University of Massachusetts Extension in Amherst recommends that to achieve optimum vent sizes, the sidewall vent area should be 15 per cent to 20 per cent of the greenhouse's floor area.

Vents with added fans allow more rapid air exchange, encouraging cooler temperatures during hot summer months.


Vents can range from crank-open window vents in glass panels, to rolling up the sides of a vinyl greenhouse. Roof vents are a standard on most models and include drip channels to control condensation. Fans can be added for additional cooling during hot summer months; heaters work with vent fans to circulate warm air during the severe cold to extend usefulness. Good ventilation is a must for plants to grow and prosper.

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