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How To Create Negative Air Pressure In Your Grow Tent.

As you already know, airflow is such a huge part of growing. If you’re growing in a grow tent or somewhere indoors, you have to take extra care to ensure good ventilation. For airflow, there are three different types of air pressure you need to know: Positive, neutral and negative.

To keep things simple, today’s post is just going to focus on negative pressure, how to achieve it and why it is important.

No matter where your plants’ habitat is, a key component to healthy growth is they always need fresh air. This critical component can be achieved in a few different ways, we are covering the most common method (extract/exhaust air system used to create the entire air flow cycle for the grow space or grow tent)

Why create negative pressure in your grow tent? 

Negative pressure offers two main benefits for a grow space. 

-When a grow space or grow tent is under a negative pressure, odour and gases released from your plants will be unable to escape the grow space without being sucked out through the running extraction system (and passing through a carbon filter if fitted) scrubbing the air, ensuring that the guy down the road doesn't know about your super-hot chillie garden.

-The other, and probably more important benefit is the negative pressure allows the grow space to "naturally" pull fresh air in. This is an easier, and simple way to have air cycling through the grow space, which is great for keeping humidity and temperature in check!

How to create negative pressure in your grow space? 

To create a negative pressure in your grow tent or grow space you will need to install your ventilation equipment in an extract/exhaust layout. We cover this style of installation here: 

For grow tents

To create negative pressure, you’ll first need to switch on your extract/exhaust fan. This will start the air exhaustion process. Wait till the fan has gotten up to speed. A clear sign that there is negative pressure in the space is when the walls of the grow tent become slightly concaved (suck inwards). Checking for negative pressure in a grow room can be more difficult as walls won't exactly "suck inwards" when experiencing negative pressure.

For grow rooms

Other ways that can indicate a good negative pressure is when the door to the grow room is hard or easy to open (depending what way the door swings) if the door swings into the space, under negative pressure the door will almost open itself into the room when releasing the door handle. While if the door opens away from the grow room it will be hard to pull open and might require some extra effort to get open.

If you’re already using a booster duct fan to encourage the intake of air, you can create negative pressure by ensuring your extract/exhaust fan is pulling more air from the space than what the inlet fan is supplying.

It is very important to remember that you still want to allow fresh air into the grow space or grow tent. Not letting in so much air that you loose your negative pressure in the space, but, enough to keep the air flowing through the room and the climate or plants happy.

Letting air into a grow tent can be achieve by opening up a duct/vent/port in the side of the tent. In some cases it is best to pop some ducting into the this port and run the ducting off somewhere that it can pull cooler air from, or where light is not going to find its way into the tent waking up your plants.

For a grow room, this inlet air can be achieved in the same way. Fitting in a grill or louvre to allow air in to the room will do the trick. You can also use ducting and run it somewhere more desirable for "fresher" air inlet.

"The larger the inlet duct or hole, the easier the air will flow in, reducing negative pressure (not a bad thing if you need more airflow!)"

However you allow air into the grow space, just ensure no light will creep in through it and wake your plants ( if they have a specific sleep cycle ).

This is just a quick guide to negative pressure. If you’re still unsure, don’t hesitate to get in touch!