Grow Tent Ventilation

Cannabis needs fresh air to grow well.

We must make sure there is lots of airflow going through our tent.

That means fresh air must enter the tent, flow through it, and get released again at the top.

So we need a good fan.

The fan inside a grow tent is mounted near the top, here.

It pushes the air out at the top.

That means fresh air is being ‘sucked’ into the tent at the bottom.

The used air could be pushed out of a window or left in your house.

It will have a strong Cannabis smell if we don’t use an air filter. (more on the air filter on the next page)

As a rule, we say that all the air in the tent should be replaced at least 2 times per minute.

The bigger your tent, the bigger fan you’ll need.

Fan Speed control

If you use a standard fan, it will run at full speed.

That is unnecesary and loud.

Because for example when the lights are off, we don’t need as much fresh air … and we can slow down the fan a bit.

That’s why we always use a fan with speed control.

Speed controlled Fan

The least expensive way is a manual speed control.

Its just a knob that you turn to change the speed.

This works fine.

But its not very sophisticated.

Automatic Speed control

A more modern way is to use an automated speed control system.

It changes the speed depending on the temperatures and/or humidity inside the tent.

If it gets hot in here, the fan goes faster.

If it gets too humid, it also goes faster.

Or when the lights switch off, the fan slows down.

That way you have a way of keeping the climate in the good range.

Which fan should I buy?

That depends on the size of your tent.

We want all the air to get exchanged about 2 to 3 times per minute.

Later we also may add a carbon filter to remove smell. They slow down the airflow and we must accomodate that.

Tent SizeRecommended Fan
up to 2ft x 2ftAC Infinity RAXIAL S4 – 105 CFM (Amazon)
Tenti Grow Tent Controller – 210 CFM (Growershouse)
up to 3ft x 3ftAC Infinity CLOUDLINE S4 – 205 CFM (Amazon)
AC Infinity CLOUDLINE T4- 205 CFM (Amazon)
Tenti Grow Tent Controller – 210 CFM (Growershouse)
4ft x 4ftAC Infinity CLOUDLINE S6 – 402 CFM (Amazon)
AC Infinity CLOUDLINE T6 – 402 CFM (Amazon)
5ft x 5ftAC Infinity CLOUDLINE S8 – 807CFM (Amazon)
AC Infinity CLOUDLINE T8 – 807 CFM (Amazon)

How to calculate exactly which fan I need?

1 Calculate the air volume in your tent (use the calculator below).

You fan should be able to exchange all the air in your tent 2-3x per minute.

If you use one or more carbon filters, you will need to add about 20% extra per filter.

Volume Calculator

This is an automated fan that will start/stop depending on the temperature.

Its a very popular model. The drawback is that it fully stops if the temperature is ‘fine’.

Tenti Controller

This controller was made for grow tents.

It changes fan speed depending on temperature and humidity.

The fan never fully stops, making sure the air won’t get stale.

Internal Recirculation Fan

Additionally, you would use an internal fan to move air around inside the tent.

The plants like some wind. It makes live difficult for pests and perhaps also reduces the risk of mild blooming on your buds.

This fan can remain on 24/7. It can get clipped to a tent pol above the led light.

Find this recirculation fan on amazon