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Ventilation equipment for hydroponics system

Ventilation is a key consideration especially when growing indoors under artificial lighting. The combination of lighting and plants generates excessive amounts of heat and humidity which will harm plants if not properly controlled.


Equipment overview

To view a basic layout of ventilation equipment see Fig 5.4 & 5.5.

Exhaust fan 

As a general rule, an exhaust fan should be capable of removing and exchanging the volume of air in the room within 5 minutes. Consult your growshop for the best fan size and type. You will need to account for the following:

-  Room size.

-  Configuration of ducting (diameter, length, junctions and bends).

-  Inlet and outlet filters.

-  The maximum temperature of incoming air.

-  Total wattage of all electrical devices in the grow room.

Where air is being moved through ducting, centrifugal/ radial (or ‘mixed inline’) fans are the most efficient (Fig 5.1). These are generally more effective at pushing air through ducting, as opposed to pulling air. Therefore, especially for long sections of ducting, position the fan at the inlet end, not the outlet (Fig 5.5).

To prevent condensate from pooling in the fan, have it mounted vertically in the ceiling as opposed to high on a wall (Fig 5.4).

Inlet fan 

This is used for pushing air into the room and helps to maximize the effectiveness and lifespan of the exhaust fan. To ensure the exhaust fan’s output is not wasted, use an inlet fan of equivalent airflow capacity.

With the aid of ducting, you can choose where the incoming air comes from. For example, in hot weather it would be better to draw air from an air-conditioned room instead of from outdoors. However, either way, be careful that the inlet air is fresh and not sourced from the same area where the exhaust air is dumped.

Where the incoming air enters the room, do not have it blowing directly onto plants, especially if its temperature is extreme. This problem can be overcome by spreading the air at the outlet point by using a ‘Y’ or ‘T’ piece (Fig 5.3 & 5.5), or a length of ducting with several holes placed in it. Additional mixing can be achieved with the aid of an oscillating fan.

A passive vent is a cheaper but less effective alternative to an inlet fan. To help maximize the exhaust fan’s output, the size of the vent’s surface area must be at least double that of the outlet on the exhaust fan.


For maximum fan efficiency keep ducting as short and straight as possible. Where junctions are needed employ ‘Y’ junctions instead of ‘T’s. If the diameter of ducting needs to change en-route, ensure this change is gradual (~10 degrees if possible).

Oscillating fan 

Usually operates 24 hours a day to ensure air is always distributed evenly, but ‘gently’, throughout the room (Fig 5.4 & 5.5). This eliminates ‘hot spots’ i.e. zones prone to CO2 depletion or excessive humidity and temperature that are most likely to occur nearest lights and dense foliage. Ensure the fan is blowing air across the top of the canopy that is located immediately below the lamp.

Additional fans may be required where multiple lamps are being used. This requirement can be determined by obtaining temperature and humidity readings beneath each lamp (see below).

Thermometers and hygrometers 

(Fig 5.6) Position the probe in the place of highest temperature or humidity. This is typically directly beneath the lights and amongst the foliage.
Where multiple lamps are being used it is best to have a dedicated meter for each lamp. Never assume that the ventilation system will work uniformly throughout the room. Having multiple meters also helps to cross check that the others are working accurately.

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Related topics


Ventilation: Equipment overview | Growroom layout | Controlling & optimizing ventilation systems

Lighting (Indoors): Lamp selection | Optimizing light intensity | Hints for setup & maintenance

Background information: Humidity | Air temperature