Grow tent ventilation – dimensional calculations and other tricks

Choosing the right grow box ventilation is essential for a successful grow.

For the beginner it may look quite complicated at first, but with a few tricks it is easy to create the right conditions for a good grow.

In this post you can find

Dimensionsberechnung für dich
Wir haben für dich die gängisten Dimensionen der Abluft-, Umluftventilatoren und Aktivkohlefilter vor berechnet. Du findest sie in unserer Dimensionsberechnung.

Pre-calculated dimensions for your grow tent

How to caluculate your grow tent ventilation correctly

Rule of thumb = All of the air in the grow box must be replaced within 3 minutes .

For a cabinet with the dimensions 100x100x200 cm, this results in a volume of 2 m³.

Since the strength of fans is usually given in m³ / h, you have to do a bit of math to get the right dimension.

Growbox Abluft Berechnen
  1. Raumvolumen Growbox = Länge * Breite * Höhe
  2. Aufschlag Aktivkohle Filter = Raumvolumen Growbox * 0,35
  3. Schlauchlänge = 1m = 1m³
  4. Puffer für die sichere Seite = 2
  5. Empfohlener Luftumschlag / h = (Raumvolumen Growbox + Aufschlag Aktivkohle Filter + Schlauchlänge) * 60 Minuten / 3 Minuten * Puffer

The best exhaust air complete sets

Wenn du dich nicht mit der Auswahl unterschiedlicher Komponenten befassen möchtest, nimm doch am Besten ein Abluftkomplettset*.

The complete exhaust air sets are made especially for newbies. The individual parts are already coordinated with each other, all you have to do is installing the set.

Of course, you can replace individual components over time, for example when you expand your grow tent or do fine-tuning.

Should you are already a professional, you’ll find the individual tube fans* and activated carbon filter * to assemble for yourself.

Eco exhaust air complete sets

Grow tent ventilation - dimensional calculations and other tricks 5

The Eco – Sets are especially for those who have no problem with the sound volume. The fans are from Ventilution * and the activated carbon filters from the long-lasting brand Prima Klima * .

Silent exhaust air complete set

Grow tent ventilation - dimensional calculations and other tricks 6

For all those who have thin walls, curious neighbors, or just like the quiet, we recommend the silent exhaust air sets * .

While the activated carbon filters are also used here by Prima Klima, the TD-Silent duct fan series from Soler – Palau * is used.

The set also comes with extra silenced ISO flexible tubes * .

Calculate the grow tent ventilation yourself

To get a suitable figure in m³ / h, we calculate an hour (60 minutes) divided by the 3 minutes in which we want to exchange the air and multiply the result by our grow tent size of 2 m³ – a simple rule of three.

That is 40 m³ / h.

Most sets contain at least one 160 m³ / h fan for such a cabinet.

We still have to take into account the heat generated by the lamp, any volume of ventilation hoses and the activated carbon filter.

For every meter of hose we add 1 m³ and the active carbon filter accounts for 35% of the room volume.

This results in the following dimensions for the grow tent size:

Assuming that we have installed a meter of hose in our closet:

“2 m³ for the cabinet + 1 m³ for the hose + 0.7 m³ for the ACF = 3.7 m³ * 60 minutes / 3 minutes = 74 m³ / h.”

Okay, so much for pure air circulation.

But what about the heat generation?

Well, at the latest here the spirits part. It depends on the type and strength of the light source. The ambient temperature also plays an important role.

So take the number calculated above, double it generously and you are on the safe side. The advantage of oversizing your exhaust air is that you have enough buffer upwards.

Et voila – you have your dimensions.

Anwender Tipp
Mit einem Drehzahlregler oder Dimmer lässt sich ein Rohrventilator super herunter regeln. Dadurch wird er leiser und verbraucht weniger Strom. Sollte es im Schrank zu warm werden kannst du ihn einfach wieder hochdrehen.

The three types of grow tent ventilation

These are the 3 different types of grow tent ventilation The supply air, the exhaust air and the circulating air. Fortunately, in our experience a newcomer to the world of growing only needs to deal with two of these three species.

Exhaust ventilation for grow tents

Exhaust air is ensured by a pipe fan that exchanges the air in your tent. To do this, it sucks in air into the cabinet and blows it out. If you don’t live far away from civilization, you will still have to have an activated carbon filter (ACF) upstream. This ensures that odors stay in the grow tent and you can’t smell anything from the outside.

To the best exhaust fans on Amazon *

The best selection of exhaust fans on *

Circulating air ventilation – so that the air does not stand still

Circulating air is ensured by a table fan, preferably with a swivel function. This ensures that the air does not stand in the closet, that there are no hotspots and that the plants do not get burned.

You can use any normal standing fan as a circulating air fan. In the best case, you can attach it with a clamp.

We recommend the Secret Jardin Monkey Fan, available at * – you can operate it with either a battery or a USB cable.

Supply air ventilation – optional

Supply air is only needed in rare cases. If the exhaust fan is too large, a vacuum can form in the grow tent and the side walls are pulled inwards. Or you have too long a way for the supply air, if you e.g. fetch it with a pipe / hose from the neighboring room.

Then you need a supply fan that blows air into the grow tent.

Anwender Tipp
Im Normalfall hat der Einsteiger aber nur seinen kleinen Schrank im Keller oder der Wohnung und da reicht der Abluftventilator und ein Umluftventilator vollkommen aus.

Why you’ll need an activated carbon filter (ACF) for your grow tent

Since cannabis develops a fairly strong odor during flowering, it is advisable to get an activated carbon filter. This filters over 99% of the odors from the air.

To do this, it is simply mounted directly in front of the duct fan. The fan and activated carbon filter are then hung inside the cabinet. The fan sucks the air through the filter and blows it out through a pipe in the ceiling of the cabinet.

We already talked about oversizing the duct fan above. Over-dimensioning the activated carbon filter can also have a positive effect. The larger the ACF, the less air resistance it has and the fan does not have to run at full load to move the desired amount of air.

However, if the fan is already large enough and does not run under full load in actual operation, you can save yourself a larger, more expensive filter. It is worth taking a look at the complete sets available on the market. These come with fans and filters that are perfectly matched to the grow tent

Circulating air for the grow tent – that’s how important it is

As mentioned above, the circulating air fan ensures that the air in the cabinet itself is moved. In the great outdoors, plants are rocked back and forth by the wind. This is important for the development of strong stems.

It would not be the first time that a beginner would lose individual plants in the middle of flowering because they could no longer bear the weight of the flowers and would twist. To avoid this, young plants should be exposed to a light wind.

But be careful not to put it directly in front of a fan, otherwise windburn can result. What happens is the following: due to the constant draft, the plant does not have time to breathe. In addition, more liquid evaporates from the leaf surface due to the constant draft.

This leads to burns and ultimately to the death of the leaf. With one leaf this may not be so bad, but with several affected leaves the plant can die. You’d better point the fan at a side wall. The wind bounces off this and is distributed in the room.

Ideally, you have a swivel fan that moves back and forth automatically. We didn’t have one, but still never had any problems. Rigid fans are also suitable. In order to still simulate wind from different directions, you can simply place it somewhere different every day.

Questions from the community

Which fan in the grow tent ?

You can use any normal table fan, ideally with a clip for attachment. It should have different speeds and a swivel function.
We prefer the Secret Jardin Monkey Fan *.

How long does an activated carbon filter last?

If you perceive a smell, it must be exchanged. Unfortunately there is no definitive month or year. The wear and tear of course also depends on how many grows you have already “chased” through the filter.

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