What Size Fan Do I Need For My Grow Tent?

If you are ventilating a grow tent, it’s important to know how much air to move to provide and adequate amount of fresh air. Since it fills up the entire space, you can guess that the volume of your grow tent is equal to the amount of air that needs to be exchanged. A little more goes into the calculation if you are filling the space with accessories.

What is an air intake fan for a grow tent?

An indoor air intake fan is a device used to bring fresh air into your grow room from outside or from a different room in your house. It’s done to cool down the air in the room and replenish the amount of oxygen and carbon dioxide in the air.

Differences between air intake and extractor fans

An indoor intake fan is essentially the same thing as an extractor fan — they can be reversed as needed and used interchangeable. However, in order to do this correctly you need to keep the strength of the air flow in mind. When installing a ventilation system in your grow room, keep in mind that the air intake fan should only have one quarter of the strength of your extractor fan. This is done to keep a balanced pressure in the room so that the CO2 and O2 levels don’t get out of whack.

Why Do You Need to Use Indoor Grow Fans?

Cannabis plants absorb all of the Co2 available around them within around one minute, which is why you’ll need to set up fans near your plants; they distribute any new air around the grow room so that all of your plants have access to a constant stream of Co2 and so that your plants aren’t affected by stagnant air, which can cause illnesses and humidity.

With just a little extra airflow, your plants will be able to breathe much better, improving photosynthesis, nutrient absorption and generally increasing your plants’ strength; the branches will grow stronger thanks to the slight wind resistance, which means that during the flowering period they’ll be able to grow thicker, heftier flowers.

At the same time expelling the air inside will keep temperature and moisture build-up under control, preventing mold and mildew from forming on your plant’s leaves, inhibiting growth.

How long should you have your air intake fan on?

A general rule of thumb is to have intake fans on for 15 minutes and off for 45 minutes in an hourly pattern. However, if you have a bit more experience you can adjust the air flow and the amount of time it’s on depending on the needs in your grow room. You’ll need to keep in mind various parameters such as humidity, temperature, CO2, O2 and the phase that your plants are in. You can do this manually by playing around with the timer of your intake fan, the strength of your extraction fan and by using a thermos-hygrometer. However, you can simplify this process by using a thermostat and a climate controller.

ECO Farm 4″ IN-LINE FANS

Features:

ECO Farm inline fan possess a blower that effectively moves the air to your target location for optimal ventilation.

It runs smoothly and quietly, and the powerful fan only outputs a noise level of 60 dB.
Durable, the galvanized steel parts are painted before leaving the factory to resist corrosion in the humid atmosphere. The compact and precise structure eliminates rattling and reduces wear, so that the components have a longer service life.

High-tech design, the device uses aerodynamically designed centrifugal impeller to provide strong airflow, while having a disproportionately low noise profile.
Multifunctional application, very suitable for cooling lighting equipment or controlling damp and heat conditions in growing tents/rooms.

Apollo Horticulture 4 Inch Inline Duct Fan

Features:

Cost-effective and high-quality. These fans are designed for resilience and include a durable steel coating coated with powder paint to prevent rust.

Low noise level: Durable plastic fan housing and blades can achieve extremely low noise (7 dB); variable speed controller facilitates adjustment of fan speed.
Convenient installation: The detachable pipe end is equipped with a locking ring, which can be quickly disassembled and maintained. The cable length is 1.6 meters, which is easy to install.

The fan also includes a built-in speed regulator. This eliminates the need to purchase separately. The speed regulator allows you to fully control all growing demands. This fan is suitable for gardeners who want an all-in-one product.

Hydro Crunch 4 inch Inline Duct Booster Fan

Features:

Household applications: Help enhance the airflow of HVAC units, remove exhaust gas and odors from bathrooms and workshops, as well as ventilate basements and attics.

Upgrade advantages: excellent balanced blade, long service life, silent operation; motor has permanent lubrication bearings, quiet operation, no maintenance; portable and lightweight; sufficient 5.5 feet of grounded power cord

Specifications:: diameter 6 inches, speed 2960 RPM, air flow 240 CFM, voltage 110/120V, power: 37W
Growing room application: used as an air intake fan to bring fresh air into the planting room; also used in small settings, LED or light under 400W lights.

How To Calculate Your Grow Room / Tent’s Fan Size

To Calculate the fan size that you’ll need for your grow room or grow tent is a relatively straight-forward process. However, before we get into those calculations — let’s take a brief look at the concepts that make up the need for having a correctly-sized extraction, and, intake fan in the first place.

First of all, having the correct fan size is something that first-time growers tend to overlook. Incorrect fan size can lead to insufficient ventilation — which is a recipe for problems during the entire growing and flowering cycle.

Here’s why;

As you may already know, plants survive on CO2 (carbon dioxide) which they extract from the air around them. When they’re first beginning to develop, the smaller-sized plants don’t need all that much CO2 because they’re not supporting a large number of leaves. But as the plants grow, the oxygen requirement increases drastically.

Consider, for example, the total surface area of your plant’s leaf. This is where your plant’s photosynthesis and transpiration takes place. The process is vital for energy provision for the plant. Young plants may only have total leaf surface area of, let’s say, 50cm2. But in a short period — maybe 30 days, the plants’ leaf total surface area may get up to 1000cm2 or more! (This is just a conservative estimate). So, in essence, when your plants are in the early stages of their growing cycle, taking good care of them is a relatively easy task in regards to providing enough CO2.

But…In a matter of time, the plants hit a specific size where optimal plant growth and development is hindered by not having enough CO2.

When plants lack enough CO2, their production drops. Indoor growers with little or no experience are often walloped when their product is affected. There are two proposed methods to fix the problem:

Better ventilation — Venting the old CO2 — heavy air out of the growing area and replacing it with fresh air.

Cooling and Supplementing — Room cooling with A.C. and adding more CO2 (with a burner or tanks of CO2).

PERFORMING THE CALCULATIONS
First, a quick note regarding measurement standards. There are two types, European and American. Below are the workings for both:

Europeans use the standards Cubic Meters per Hour (M3/H) when measuring their extractor fan size. 
In North America, extractor fan size is measured in Cubic Feet per Minute (CFM).
 Let’s take things a little further for you to understand the difference between the above two standards:

For Cubic Meters per Hour (M3/H) …

You need extractor fan size in meters per hour. That is, the volume of active growing area in meters multiplied by 60 then multiplied by 1.33.

A quick, simple example;

Suppose your growing tent measures 10ft long, 8ft wide, and 8.5ft tall. The first step is to convert your measurements into meters. 1ft = 0.3M. Our new measurements will be 3M by 2.4M by 2.55M, which gives 18.36M3 as the total volume in cubic meters of the growing area.

As mentioned above, the total volume is multiplied by 60, then by 1.33. Why? We multiply by 60 because our equation is in meters per hour and we need the number of air changes per hour. We then multiply by 1.33 to allow for the use of a carbon filter attached to the extractor fan. The 1.33 takes care of the drop of efficiency of approximately 0.25 or 25% once we assign a carbon filter. Note that 0.25 is subject to change depending on several factors such as the age, make, and length of the screen, among others.

For the Cubic Feet per Minute (CFM) …

The workings here are quite straight forward. Using our previous tent measurements of 10ft by 8ft by 8.5ft, we can get the required fan size by performing the following calculations:

Note that there’s no converting the units into meters as we’ve already got the feet measurements as the base dimensions.

The volume of the active growing area = 10ft by 8ft by 8.5ft by 1.33 = 904.4 CFM.

Please ensure that …

You work out the correct calculations whether you’re working with European or American measurements. 
Look at the fan’s specs before buying, and, ensure that the CFM is enough for your grow room or grow tent.

The proper size fan for a 4x4 grow tent:
Let me give you an example calculation for a 4x4 grow tent, which is a pretty common size among indoor growers:

Most 4x4 tents measure 48in x 48 in x 80 in. So the total volume of air in a 4x4 grow tent is 4ft (length) x 4ft (width) x 6.667ft (height) = 106.67 cubic feet. But that doesn’t mean you need a 106 cfm fan.

When you consider a carbon filter reducing your fan efficiency by 25%, and one 90 degree duct bend reducing another 30%, a fan with 215cfm will get reduced to ~112cfm (200cfm x 0.7 x 0.75).

So for a 4x4 grow tent with an area of ~106 cubic feet, a grow tent fan (inline fan) rated for ~215cfm would get the job done.

Conclusion

Figuring out the correct fan size for your grow tent might seem complicated, but it doesn’t have to be. If you follow the rules of thumb we gave you above, you’ll end up with a fan that effectively removes all excess heat from your tent, whether you have a huge grow tent or a mini grow tent.

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