FREE Delivery Over £50*

ClearPay - Pay in 4

Best Price Guarantee

Excellent Excellent 5 star yotpo rating

Chat to an Expert

Air - Your Grow Room's Atmosphere

Air - Your Grow Room's Atmosphere

Alex Grady

What is Air?

Air (or atmosphere) is the gaseous envelope that surrounds this planet.

It's mostly of a mix of gases, but also contains solid and liquid particles. The two main catagories are:


Non Variable components

  • Oxygen (21%)
  • Nitrogen (78%)
  • Other gases like: Argon, Neon, Krypton, Hydrogen, Xenon, Radon in very small amounts

Variable components

  • Carbon Dioxide (0.03% variable)
  • Water (vapour, liquid) Dust, Smoke, Smells

As you can see, oxygen and Nitrogen make up 99% of air! Well, the laws of physics affect them like they do any other gas or liquid.

There's a direct relationship between temperature, pressure, volume and density. Any change in one means a corresponding change in all the others.

The change is always the same and is always predictable.

By understanding the relationships between each of these factors (and how it affects plants), you can really fine tune your environment.

When air is heated & cooled

When air is heated:

  • its volume increases (it expands)
  • its density decreases (it becomes lighter)

This means that there's a fall in pressure. When this happens, the amount of water vapour it can hold increases.

Conversely, when air is cooled:

  • its volume decreases
  • its density increases

This means there's an increase in pressure, and the amount of water vapour it can hold decreases.

Heating & humidity

So, heating air makes it expand, which means it can hold more water.

So far, so good.



If the air you're heating has a set amount of water in it, as it expands, the relative humidity drops.

This sounds complex, but it's not...remember, your RH tells you how full of water your air is, as a percentage (%).

As your air warms, it has the same amount of water, but is less % full of water, simply because it can hold more water.


Imagine you have a 1L jug of water - with 500ml of water in it, it will be 50% full.

If you stretched the jug to 2L, and it still has 500ml of water in it, it will be 25% full.

That's how it works with air - heating air is like stretching the jug.

Of course, when you use high intensity lights, a lot of heat is generated. Make sure you've got a good air exchange system. If this isn't enough to keep your humidity in check, you may need to humidify your air.

Cooling & humidity

It works in reverse, too.

When air is cooled, it contracts - if it has the same amount of moisture, the relative humidity increases.

If you keep cooling, eventually you'll reach the dewpoint temperature. This is the point at which your air is 100% full of water.

When this happens, visible water droplets start to form.

This is why you sometimes you get condensation in your grow room after the lights go off and the room cools.

Again, good air exchange can prevent this from happening. Failing that, there's always dehumidifiers!

Carbon Dioxide

Without CO2, photosynthesis can't happen.

Since plants use CO2 you need to exchange air to keep levels high.

Fortunately, CO2 is a variable component - you can increase CO2 levels. Normal atmospheric levels are around 350ppm. Air inside your home can be as high as 800ppm, just from people breathing.

So, that's annother good reason to use input air to your grow room from indoors.

It's been found that plants can cope with CO2 levels of up to 1200ppm! Don't be afraid to add CO2 - MyCO2 Bags are an easy and affordable option.

myco2 bags

Leave a comment

Please note, comments need to be approved before they are published.