The right ventilation for the grow room

Supply air - Exhaust air - Fan strength - Recirculated air

Just like lighting and fertilisation, ventilation is one of the elementary elements of indoor growing. Proper ventilation consists of 3 elements: the supply air, the exhaust air and the circulating air (ventilation). Used air must be transported out of the growroom via an exhaust fan (possibly with an activated carbon filter). This allows fresh air (oxygen and CO2) to flow in, which is absolutely necessary for plant growth due to photosynthesis. By moving the air in the room with fans, there are no hot spots and the fresh air is evenly distributed in the room.

Climate in the growroom, activated charcoal filter when growing

Tube fans with an activated carbon filter are usually used to ventilate the growroom.

Supply air - fresh air for the growroom

To thrive perfectly, plants need oxygen and carbon dioxide, which is fed into the growroom from outside through the supply air. As a rule, 1-2 supply air openings are sufficient, which should be located on the opposite side of the exhaust air and are best secured with a close-meshed net against the penetration of pests.

However, there may be cases where the use of a fan for the supply air becomes necessary:

  • The supply air must be drawn in from another room at a greater distance, as the air in front of the grow box is too warm.
  • The exhaust fan is so powerful that it creates a "negative pressure" in the box and it contracts the walls

If the supply air is drawn in via a fan, the fan for the supply air must have less power than the one that conveys the air out of the growroom (exhaust air). For the supply air, simple Axial fan fans are best.

Exhaust air - the stale air must go out

Used air is removed through the exhaust air. This also cools the growroom, as the lamps produce a lot of heat. The extraction of the used air in the growroom through a Fan is absolutely necessary. Used air is thereby removed and replaced by fresh air. In addition, the use of a Activated carbon filter prevents the spread of odours outside the room. It is also possible to control the entire climate via this. For more see How can I control the climate in the growroom?

Choosing the right size fan for the ventilation system is very important for the success of indoor growing. In general, one can assume the following Growboxes and grow tents the following fan dimensions can be assumed:

Box surface 125W 200W 250W 400W 600W 800W 1000W 1200W
60×60 cm 105 m³/h 185m³/h 225m³/h
70×70 cm 185m³/h 225m³/h
80×80 cm 225m³/h 325m³/h
90×90 cm 225m³/h 325m³/h
100×100 325m³/h 680m³/h
110×110 325m³/h 425m³/h
120×120 325m³/h 425m³/h 680m³/h
130×130 325m³/h 425m³/h
140×140 325m³/h 425m³/h 680m³/h
150×150 425m³/h 680m³/h
160×160 425m³/h 680m³/h
170×170 425m³/h 680m³/h
180×180 425m³/h

This is based on experience and can vary up and down. The hotter the ambient temperature, the more volume you need. For small growing spaces, more volume is more likely to be needed.

Another approximate calculation rule is based on the room volume. This formula is rather intended for larger, self-equipped rooms (for grow cabinets such as the Homebox, the above formula based on the lighting is more recommended, as the heat problem is much more dominant there).

This formula looks as follows, an example calculation is given in brackets:

  • Determining the room size: height x width x depth of the room (e.g. 2m x 2 m x 2m= 8m³)
  • Surcharge for the activated carbon filter: the ACF reduces the performance, therefore you have to add approx. 35 % of the room volume for it (8m³ x 0.35= 3m³).
  • Surcharge for the air hose: approx. 1m³ per running metre (so 3m³ for 3 metres of hose).
  • Calculation of the extraction volume: The calculated volume is multiplied by 12, in confined spaces (grow cabinets) multiply by at least 30 due to the high temperature.
  • The formula is therefore as follows: 12 x (room volume + allowance for activated charcoal filter + allowance for air hose) = necessary capacity of fan
  • Result of the example: 12 x (8m³ + 3m³ + 3m³) = 168m³/h.

Odour prevention through activated carbon filter

By attaching an activated carbon filter (ACF), the occurrence of the often very strong odour can be avoided. This prevents curious neighbours from becoming aware of the grow. AKFs are filled with activated carbon, which draws the odours out of the exhaust air. Note that by using an activated carbon filter, the performance of the fan decreases because there is more resistance. In the following you will find the appropriate ACFs for the respective fan performance:

Design of an exhaust air system

Ventilation

The activated carbon filter is located in the growroom. It is connected to the fan via a hose, which sucks the air from the filter and transports it outside.
The fan can also be installed outside the grow area, simply by making sure the hose connecting it to the filter is long enough to take it outside the grow area. If you install the fan inside the grow area, you still need to direct the extracted air outside by attaching another hose to the output of the fan and leading it outside.
There are HosesThere are also sound-insulated hoses that minimise the noise. In addition, at the end of the exhaust air you can also Silencer at the end of the exhaust air to reduce the noise caused by the outflowing air.

FanRecirculating air - the air needs movement

In addition to exhaust and supply air, permanent recirculation of air by Fans is essential. Moving the air in the growroom prevents hot spots from forming under the lamp and also ensures that all the air can be exchanged. Especially when the plants are close together, zones could form under the leaves without fans, where no exchange takes place and the plants do not have enough CO2 available. In addition, especially Indicas tend to blossom rot (botrytis) towards the end of the flowering phase, when their buds become fat and compact. This can be prevented by sufficient fresh air at the buds. How many fans are used in the grow room depends on the conditions and the size of the grow room. In any case, at least 2 fans should be Fans should be installed. Swivel fans, i.e. oscillating fans, are particularly recommended, because this ensures an even and distributed movement of the air, just as it does in nature.

Cooltube - dissipating the heat from the lamps

Especially in summer and in very small growrooms, the high temperatures of the sodium vapour lamps can easily cause a heat build-up in the grow room. A very effective method to avoid this is the use of a Cooltube. This is either integrated into the existing exhaust air system or, even better, operated as a separate system with an axial fan. The exact construction can be seen in the sketch.

Connecting the Cooltube correctly

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