Easy Grow Room Ventilation Setup 101 All You Need To Know

Easy Grow Room Ventilation Setup 101 All You Need To Know. Ventilation is essential in your grow room. It provides much needed fresh air and constant supply of CO2 to your plants. It also helps to keep humidity and temperature under control. Excessive humidity and heat could be harmful to your indoor garden. HID lamps can overheat your tent very quickly, and a ventilation system is necessary to extract this hot air.

All you need to know about grow room ventilation
Easy Grow Room Ventilation Setup 101 All You Need To Know

Why Do We Need Grow Room Ventilation?

How do water and minerals get to the leaves? although roots can exert a slight upward pressure, it is evaporation of water from leaves a process called transpiration that moves water molecules and ions up from the roots.

Transpiration exerts a pull that is related downward along a string of water molecules from leaf to root. Hydrogen bonds cause water molecules to stick together a phenomenon called cohesion as each water molecule evaporates it pulls on the next water molecule and it pulls on the next this relays the pull of evaporating water molecules all the way down to the roots.

The adhesion of water two walls of the xylem cells helps to keep gravity from pulling the water molecules back down as each water molecule escapes from the leaf it pulls a column of water molecules upward solutes are transported along with the water thus the plant xylem uses the movement of evaporating water molecules

Cohesion and adhesion to draw water and dissolve minerals from the soil into its roots and upward to its leaves hot dry windy conditions increased transpiration if not enough water moves up from the soil to replace the water lost to evaporation the plant will wilt and it could die how does a plant prevent excessive water loss?. An opening in a leaf is called a stoma.

Stomata are generally open during the day to allow carbon dioxide into the leaf where it is used in photosynthesis while the stomata are open water moves out of the leaf by transpiration this allows the plant to move water and minerals to the leaf and the evaporation of water also functions to cool the plant if hot dry conditions require the plant to conserve water

guard cells close the stomata. This is a trade-off although closing the stomata reduces water loss this also slows down photosynthesis and may cause the plant to overheat

Fans sizes and types:

RVK grow room extractors
RVK grow room extractors

Wolfnado fans have a switch to be used either as an intake or as an exhaust fan

RVK fans come in 2 types:E2 and L, as well as in different sizes: from 4” to 12”

E2 refers to intake fan, and L is the exhaust fan. They normally come in a pair, so it’s best to select an A and L of the very same size, to ensure negative pressure in your grow tent. Some fans included a switch that transforms them into A or L type (Wolfnado). Remember to always pick a set of both type E2 and L of the same size to attain negative pressure.

Fan Code Fan Size Capacity(M³ Per Hr)
RVK Sileo 100E2 100mm (4″) 184
RVK Sileo 125E2 125mm (5″) 220
RVK Sileo 125E2-L 125mm (5″) 323
RVK Sileo 150E2 150mm (6″) 428
RVK Sileo 150E2-L 150mm (6″) 720
RVK Sileo 200E2 200mm (8″) 796
RVK Sileo 200E2-L 200mm (8″) 1008
RVK Sileo 250E2-L 250mm (10″) 1080
RVK Sileo 315E2 315mm (12″) 1375

Ventilation and Negative pressure

A slight negative pressure is what you want to establish in your tent or growing room. This means that there is slightly more air going out than coming in the grow room. If you are growing in a tent you should see the sides pulling a little bit inwards. This is great, as the negative pressure will help to remove excess humidity and temperature from the tent. It also keeps odors under control.

What you definitely do not want is positive pressure (more air coming in than going out). In this case, you will quickly see your tent inflating, and it will lead to odor leaks.

Capacity between type E2 and L is around 40%, so always choose a set of same size E2 and L fans to be sure to achieve the negative pressure. (Even if 10% are lost through the filter, and a couple more percents through ducts, this will surely be good enough).

Forced and passive ventilation

Forced ventilation is when you “force” the air to come in and out of your grow space, for this you will use 2 fans: one intake and one extraction.

Passive ventilation is when you have had a vent in the tent to let the air in and an exhaust fan working actively to extract the air. This is a cheaper but less effective way to ventilate your grow room. If you want this setup, your vent surface will need to at least double the size of the outlet of the exhaust.

Fan capacity needs

Ideally, the air within your grow tent should be renewed at least 20 – 30 times per hour (or every 2-3 minutes).

With this rule in mind, it’s possible to calculate which fans you need according to the size of your room or tent.

The wattage method

The best method and the most accurate way to calculate this is taking into account the wattage of your room.(wattage/2)+ 10% of the original wattage
So, for example, if you are using 400 wattages:

(400/2) + 40= 240m3/h
The result will give you the size of the extract fan needed. Round up to the closest fan available and over-engineer it by one size. It’s always better to overestimate the flow rate than being too short.

With the above calculation the Systemair 150 Amm RVK Fan, for example, would be a suitable choice. Get the type E2 for intake and L for extract, this is to achieve a negative pressure inside your tent.

The Dutch method

The second way to calculate fan capacity needs is known as the Dutch method and takes into account the volume of your grow tent, not the wattage.
Let’s take the example of a 2.4m x 1.2m x 2m tent (Grow Cube Pro Tent 241)
This is also assuming you are using proportionally:

  • 400W for a 1m x 1m
  • 600 W for a 1.2m x 1.2m
  • 1000W for a 1.5m x 1.5m

1. Calculate the volume:

Volume = 2.4 x 1.2 x 2 = 5.76m3
2.Multiply by 12 ( as this is how many times per hour you want the air to be renewed)

5.76 x 12 = 69.12
3. Multiply by the number of lights (this is supposing you are using 600 watts lamps)

The grow cube pro tent can accommodate 2x 600 Watts lamps)

69.12 x 2 = 138.24 m3/h is the capacity of the intake or inlet fan that you need in perfect and stable conditions.
4.Choose a fan of the closest higher capacity and over-engineer it off one size. It’s always better to overestimate the flow rate than being too short.  With the above calculated the Systemair 200 Amm RVK Fan, for example, would be a suitable choice. Get the type E2 for intake and L for extract, this is to achieve a negative pressure inside your tent.

Noise control

Yes, fans are noisy, and you just cannot get away from this. However, there are a few steps to follow to silence your fans by around 20%.

  • Use a rigid silencer. They help to reduce the noise levels and come in different sizes to fit your fan.
  • Replace your ducting with acoustic material to reduce airborne noise from the air hitting the duct walls.
  • When running fans at 60 or 70% of their capacity, another further 10 decibels can be taken away from the noise level.
  • Consider setting up 2 x 5” fan system instead of a 8” one. Air capacity is the same, but as decibels don’t add up, you can reduce the noise pollution considerably. A 8” is around 90 decibels and a 4” around 50 decibels. 2 sets of 4” would probably give you around 55-60 decibels which are 30 less than with a 8” one only.

TIPS on ventilation:

Easy Grow Room Ventilation Setup 101 All You Need To Know
Easy Grow Room Ventilation Setup 101 All You Need To Know
  • A Fan speed controller is essential for optimal growth of your plant. On a hot day, it will automatically increase the power of your fans to obtain adequate temperature and humidity. In colder weather, the fan will be appropriately slowed down. It’s all hands-off hence much easier with one of those to have the best growing conditions possible.
  • It’s always best to step up one size of fan than choosing a smaller one. For example, if after calculation you need air to move at 310 m3/h in your tent, choose a fan with a capacity of 400m3/h. It will always be useful during hotter days. Plus, in normal condition it will be allowed to run at a reduction of 30 to 50%, to reach the quiet pitch!
  • There’s a great advantage to using a fan setup with an air cooled light. Using one of those will enable you to step down one size on the fan and permit a better control of humidity. Moving too much air can lead to an arid environment.
  • If you are using an air duct to direct your airflow, keep in mind that the longer the duct the less effective the fan becomes.  2% of fan capacity is lost for every metre of ducting!


  • If the air temperature is still too hot, humidity is rising, or you can see mildew, mold or bud rot in your indoor garden then there is probably not enough ventilation and you need to review your fans capacities.
  • If temperature and humidity are too low, then you probably have too much air movement inside your growing space.

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