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Choosing the Right Extractor Fan for

your Grow Room

Ventilation andEnvironmental Control

INFOSHEET 10401:

VOLUME 1:INDOOR GARDENING FOUNDATION

Introduction

When growing indoors, environment is everything! A successful

grower needs to take practical steps to manage factors such as

light levels, temperature, relative humidity and CO2levels. Here we

introduce the role of extractor fans and environmental controllers

used by indoor gardeners to maintain the ideal indoor environment

for their plants.

Calculating your Fan Requirements

So Which Size Fan do I Need?

Calculating the Active Growing Are

Growers use extractor fans to keep the afresh (and CO2 levels rich) in their growrooms. Extractor fans come in differenshapes and sizes. They are rated in terms othe amount of air they can move in a give

time period. In North America extractor fanare rated in cubic feet per minute (CFM.)

The volume of the active growing area is thspace taken up by the lights and plants, not thwhole room. To work out this volume simpmultiply the length x width x height of thactive growing area. Lets take an example

For the majority of indoor gardens withouAC or supplementary CO2, a common gois to exchange all the air inside your growroom once per minute. However, its wise t

add 25% to allow for a drop in the extractofans efficiency if using a carbon filter. Thfigure is not fixed; it depends on the makand age of the filter and the length ancourse of ducting between the fan and filteand many more interesting factors.

If we run this equation through our exampabove our required CFM is 328:

There are many ways to work out which sizextractor fan is needed for your grow roomSome rules of thumb are a little too basicwhereas others can be overly complicatedThe following method is very popular anstraightforward and has served many growerwell. We start with this general formula:

Choosing the Right Extractor Fan

Minimum Fan Size Required (in CFM)=

Volume of Active Growing Area (ft) x 1.25

8'

8.2'

4'

Total volume:(4 x 8 x 8.2)

262.4 cubic feet

262.4 x 1.25 = 328 CFM

Volume of ActiveGrowing Area

25% efficiencydrop

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Choosing the Right Extractor Fan

Choosing the Right Extractor Fan Essential Equipment

Why not just go BIG?

Maximizing Efficiency

Passive vs. Active

Some growers believe the maxim bigger is better naturally applies to extractionfans but this is not necessarily the case. Yes, extracting air from your grow roommeans youre removing hot air, but youre also removing humidity at the sametime. This means that an over-sized extractor fan can sometimes cause lowrelative humidity. This, in turn, creates a host of negative effects that will lead topoor plant growth.

Increasing the size of your extraction fans is not always the way to combat heatproblems in your grow room. This is especially true in the summer months. (Ifthe air youre pulling into your garden is already warm then your room will staywarm.) If you cant keep the heat down and youre changing the air in yourgarden more than three times each minute, you need to consider installing airconditioning or using air-cooled grow lights. (See Pro Tools box, right.)

Growers use ducting to channel the air moved by their extraction fans. Insure thatall ducting is securely fastened to extraction equipment. The smallest leak (especiallythose near the extraction fan) can severely reduce efficiency.

Its also important to plan the route from your extraction fan to the outside world/ venting area. The shorter and straighter the better. Any bends in your ductingcost you more efficiency reductions. For example, a 30 bend in ducting cuts theamount of air flow by 20%. A 90 bend constricts air flow by as much as 60%!

Oscillating fans (i.e. fans that just circulate the air within the active growing arearather than extract) help to insure that air quality is even throughout your grow room.

When you remove air from your growing area you create negative pressure. Inother words, you create a pulling effect which brings fresh air into your indoorgarden to replace the air thats being extracted. Some growers simply rely onvents and allow fresh air to be passively pulled in through the equalization of airpressure. Other growers use a smaller, secondary fan to actively blow fresh airinto the growing space. Smaller input fans are preferred by indoor gardeners asthis maintains a slight negative pressure in the growing area which makes yourgrowing environment easier to manage as a whole.

Pro Tools

Ideal AirDehumidifier

Ideal AirPortable Air Conditioning Unit

Titan Controls Kronus Series

Environmental Controller

Sun SystemsAir-Cooled Grow LightReflectors

Bug Screens (for incoming air)

Min / Max Thermometer and HygrometerExtraction FansFan Speed ControllerPhreshFilter

Other Things To Consider

This final figure is the minimum size extractor you willneed. If your garden is in a very well insulated loca-tion (such as a basement) using this figure should befine. If your garden is located in a sun-exposed loca-tion such as a south-facing upstairs bedroom or an

attic then the extractor size may need to be increasedagain by 25%. Of course, you will have to match yourrequired extractor size to the nearest size available. Inthe previous example overleaf the nearest widely avail-able inline fan size is a 6 (150mm) 390 CFM extractor. 12'

8.2'

8'

Total volume:(8 x 12 x 8.2)

787.2 cubic feet

787.2 x 1.25

= 984 CFM

Volume of ActiveGrowing Area 25% efficie

drop

Heres another example witan active growing area thretimes larger.

In this indoor garden thnearest widely available fasize available is a 12 (315mm1000 CFM extractor.

For grow tips, expert advice, and educational videos check out

JUST4GROWERS.COM

10202Installing and running air-cooled grow lights10402Introduction to environmental controllers10302Relative humidity and vapor pressure deficit

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