How To Ventilate Your Grow Room like a Pro

A1M Hydro is delighted to welcome our new guest blogger, Rich Hamilton! Rich is well known in the industry for his expertise and comprehensive Growers Guide books

In the first of a mini-series, Rich looks at a different aspect of the growing process, delivering some hints and expert tips that will surely prove to be valuable, no matter if you’re a complete newbie or an experienced grower.

In his first blog, Rich takes a closer look at grow room ventilation. Let’s dive straight in…

Grow Room Ventilation

Ventilation in the Grow Room-a Beginners Guide

When you are setting up a grow room there are lots of things to consider but one of the most daunting to understand is ventilation, If you get it right it is the key to success. Get it wrong and you will see your plants suffer and pests thrive! 

So lets go through the process from the beginning

Why do I need ventilation?

In a sealed environment your plants consume CO2 for photosynthesis and release moisture. 

This is a problem as too much heat and moisture stagnates air, halts growth and increases humidity. This produces the perfect conditions for mould, fungus and pests to thrive. Your plants also like to “breathe” fresh air.

What is a ventilation system.

Ventilation extracts stale, hot, humid, smelly air out of your grow room and draws fresh air in, controlling temperature, humidity, pests and CO2 levels.

Your ventilation system should comprise of at least the following components.

Outtake (extraction) fan

This draws hot, stale, humid, smelly air out of your grow room. Your goal is to extract more air OUT than you are drawing in (negative pressure) to stop the tent becoming too full of air and odours from escaping elsewhere. For this reason your outtake fan should be more powerful than your intake fan. Your extractor fan should be positioned high, towards the back of your grow room.

Ok, so how do I work out what outtake fan I need? 

Extractor fan size is measured in M3/H, which is the amount of air in cubic meters that the fan can remove per hour.

The basic calculation to get this figure is  (Volume of active growing space = (m) x 60)

To get this figure, multiply your tent’s/growing enviroment’s dimensions

 (length, width, height) together to get the total volume.

For example, we are using a 1.2m x 1.2m x 2m tent so that is 1.2m x 1.2m x 2m  = 2.88 cubic metres. 

2.88 cubic metres is therefore the volume of air that your tent holds at any one time.

To identify the perfect outtake fan that is able to remove this amount of air from your grow room every minute you multiply this number by 60 (minutes) to get the desired hourly rate.

2.88m x 60 = 172.8 M3

For some growers with a simple set up this serves as a good base figure for what minimum power outtake fan they should buy.

It is recommended however that to be more accurate and make your ventilation system more efficient that you should account for any variables in your grow room which can affect fan performance.

These variables can be taken in to account as follows.

  • 600W HID Lights- Add 5% per air cooled light or 10-15% per non-air cooled light.
  • CO2- Add 5% for rooms using any CO2 enrichment product
  • Filters- Add 25% if you are using a Carbon filter as part of your exhaust system
  • Temperature- Add 20% if your tent is in a warm place such as an attic or the seasonal climate is quite hot. Minus 15% if your tent is in a cold place such as a basement or the seasonal climate is quite cold.
  • Ducting- Add 5% for every 5 feet of ducting used. Add 20% for every bend of 90 degrees or more in the ducting.

Here is an example.

We are using a 1.2 x 1.2 x 2m tent.

We are using  2 x 600w lights (non air cooled)

We are using a carbon filter

We are using a CO2 enrichment product 

Our tent is in a warm attic

Our ducting is 10 feet long with 1 bend of at least 90 degrees

So…the basic volume calculation is as follows.

Room volume = 1.2×1.2x2m=2.88

2.88 x 60 = 172.8 M3/H

 Now we add the extra %’s from our grow environments specific variables.

172.8 + (172.8 x 20% for the 2 non air cooled lights)= 207.36

207.36 + (172.8 x 5% for the CO2 enrichment product) = 216

216 + (172.8 x 20% for the Carbon Filter) = 259.20

259.20 + (172.8 x 10% for the ducting length of 10m) = 319.68

319.68 + (172.8 x 20% for the 1 bend of 90 degrees or more)= 354.24

This gives you a final figure of 354.24 (rounded up to 355) M3/H and means that you will need an outtake fan with a minimum of this power in order to replace all the air within your growing environment every minute. You can match to the nearest power fan as long as it is higher than this number but not lower. 

In this case a 6”inch RVK fan would be a great match with its capability of delivering a maximum air flow of 428M3/H.

Note that you will need to match your required extractor fan size to the nearest size available in terms of the size of your ducting for best performance.

Intake system (fan, ducting, connections)

This actively draws fresh air into your grow room.  

How do I work out what intake fan I need?

Choose a fan that’s 15- 20% less powerful than your extractor fan. This ensures that you are keeping lower levels of air entering the room than you are extracting from it, keeping your tent in negative pressure. This is important as otherwise your tent can overfill and unfiltered air can start seeping out of vents, ports and zips. 

Your Intake fan should be positioned at the bottom of your tent on the opposite side to the extraction fan.

What else will I need to assist my ventilation system.

Fan controllers

Speed fans up when grow room becomes too hot. 

Slow fans down if grow room is too cold

Air Circulator Fans

These are oscillating fans used to move air inside your grow room. 

Never aim them directly at plants, as this can cause damage.

Temperature And Humidity Meter

This reads how hot and humid your grow room is 

You should aim for a humidity of:

70 – 85%  in Propagation

65 – 75%  in Veg

45 – 65%  in Flowering

And a temperature of:

Lights on temperature of 24C – 27C

Lights off temperature of 21C – 24C

So there you have it, a crash course in air extraction systems. Hopefully now you can buy in confidence knowing what you need. Remember though, when in doubt ask an expert for advice as this is one factor of your grow regime that you really can’t afford to get wrong!

By Rich Hamilton


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