How to Get your Climate Spot On

How to Get your Climate Spot On

19 May 2017

Controlling your climate doesn’t have to be hard. Here’s everything you need to know.

The Ideal Climate

It depends on what you're growing, but as a rule, you should aim for:

  • Temperature: 24oC- 28oC (day/lights on) or 22oC - 23oC (night/lights off)
  • Humidity (RH): 70 – 85% (propagation), 65 – 75% (veg), 45 – 65% (flowering)
  • CO2 level: 1000ppm - 1200ppm for up to 40% faster growth

Standard Vs. Closed Loop Rooms

There's no right or wrong way of doing it - it just depends how much control you want, and what your budget is.

Standard Set Up

To keep your temperature, humidity and CO2 levels under control, you extract stale air and draw fresh air in. 

You’ll probably need a heater in winter. In summe, you'll need to extract more air, but be warned, your grow room can never be cooler than the air you're drawing in, if you rely solely on air exchange.


BudBox Grow Tent in Coleshill BudBox Grow Tent in Coleshill
BudBox Grow Tent in Coleshill
  • Easy to set up
  • Inexpensive
  • Your control is limited to outside conditions
  • You can get climate fluctuations
  • Pests are a bigger problem
  • It can be noisy if you move lots of air

The equipment you need depends on your set up. 

Standard set ups largely rely on air exchange. For this, in a small room, all you strictly need is an extraction system and heater. 

  • Extraction System (fan, filter, ducting)
  • Heater (winter)
  • Additional spot cooling & air circulation fans (summer)
  • Air conditioning (summer)
  • Carbon filter (odour removal)
  • CO2 equipment Humidifier Dehumidifier

Closed Loop Set Up

Closed loop growing spaces are almost completely sealed off.

Hardly any air enters, hardly any air leaves. Rather than exchanging air, you constantly treat the air that’s already in your grow room.

Why bother? You get complete climate control (temperature, CO2 levels, humidity, etc.) while keeping pests and diseases out!

Closed Loop Room Coleshill Closed Loop Room Coleshill
Closed Loop Room in Coleshill
  • Plants grow in their ideal climate all year
  • No temperature or humidity fluctuations
  • Pests struggle to get in
  • No temperature or humidity fluctuations
  • Optimum CO2 levels
  • Growth is better, yields are bigger
  • Initial cost is more

You don’t need an air exchange system. Instead, you treat the air that’s alreadyin your grow room. As a bare minimum, you need to cool, heat, add CO2 and remove humidity. 

Most people opt for a climate control system for basic functions. A Kahn system will cool & heat your grow room without taking up mich space. 

  • Air conditioning (summer)
  • Heater (winter)
  • CO2 equipment
  • Dehumidifer
  • Humidifier
  • Carbon filter (odour removal)
  • Air circulation fans
  • Small extractor kit (for negative pressure & filtration – also a power loss back up) 

Choosing an Air Extraction System

What you need will depend on:

  • Your lights
  • The size of your grow space
  • The time of year (more air needs to be extracted during summer months)

As a general rule, the more lights you have, the better your air exchange system needs to be.

If in doubt, it's always better to overspec than underspec.

Extractor Fans

Extractor fans draw air out of your grow room. You need one that extracts enough air. 

To work out how much air it needs to extract:

Eco Extraction Kit Eco Extraction Kit

Step 1

Multiply your tent's L x W x H

The answer is how much space is covered by your grow lights


In a XL BAY6 Tent:

1.2m x 1.2m x 2m = 2.88m3

2.88m3 is the total area covered by your lights.

Step 2

Multiply this by 60

That'll tell you how much air to extract every hour.


In a XL BAY6 Tent:

2.88m3 x 60 = 172.8m3

100mm (4") RVK100 would do the trick!

Step 3 (optional)

To be really precise, you can:

  • Add 20% for a warm attic
  • Add 20% if using a carbon filter
  • Minus 15% in a cool basement
  • Add 20% for long ducting
  • Minus 25 - 30% for air cooled lighting

Intake Fans

If you’re only extracting a small amount of air, you can get away with using vents to passively draw air in. 

If you do need an intake fan, make sure you draw in less air than you extract. Otherwise, you can end up overfilling your tent, and unfiltered air will start seeping out. 

Method 1 (easiest)

Use an intake fan that’s 25 - 30% less powerful than your extractor fan and run them at the same speed. 

Method 2

If both fans are the same size (not recommended), run your intake fan at a slightly lower speed than your extractor fan.

Top Tips

  • South facing rooms are hotter than north facing rooms, so you might need a bigger extractor fan.

  • Remember that your fans should be placed at opposite ends of your grow room so you don’t extract air that has just been drawn in

  • If you’re torn between two size fans, buy the bigger one and run it at a slower speed

  • Use Expando Tent Supports to stop your tent walls being sucked in by your fan

EC vs. AC Fans

EC fans cost more to buy, but are so much cheaper to run that you make back the cost of the fan after just a year.

After 5 years, you'll have saved up to £1,380! Fact. Really, see the number crunching we did. 

AC Fan + Step Transformer Controller:

AC Fan AC Fan

£324.06 energy a yr!

AC Fan + Resistor Controller:

EC Fan EC Fan

£189.06 energy a yr!

EC Fan + Controller:

AC Fan AC Fan

Just £49.95 energy a yr!

Fan Controllers

Unless you want your fans to run at full power all the time (nobody wants that), you need a fan speed controller. They speed fans up or slow them down to get your temperature bang on.

To make sure enough air is extracted to maintain your CO2 level and humidity, you can set your minimum fan speed.

The controller you need depends on your fan:

AC Fans

AC fans need an AC controller

  • Voltage controllers 
  • Resistor controllers (noisy when used to slow fans)
  • Dynamic frequency controllers (reduce running costs)

EC Fans

EC fans need the same brand EC controller

Choosing an Air Conditioning System

There are a couple of kinds to choose from. All are easy to set up, if you know what you're doing. Before buying, give us a call, so we can help you choose and install the right unit.

Split Air Cooled Systems:

  • Indoor and outdoor unit
  • No water needed – can be a huge cost saver

Khan Climate Control Systems are split systems and are stupidly easy to install. Units are so light that you'll easily get them into tight spaces, too. 

Water Cooled Systems:

  • Water cooled system – they’re basically the opposite of a radiator
  • Indoor unit only – great if you’ve not got space for an outdoor unit

The OptiClimate Water Cooled Systems have water running through them to cool the air. Cold tap water goes in, and hot water goes down the drain.

Which is Cheaper to Run?

The real question is: How you pay your bills?

If your water bill is fixed, the water cooled system is a good option. If you’re on a water meter, a split system is better.

Kahn Climate System In Store Kahn Climate System In Store

What Size Unit?

Most manufacturers tell you how many lights each size air con unit can be used with. For the ones we sell, you can use them with:

See them in Action!

Working climate control systems are on display at all stores! Call your local store for more information or to book an expert consultation.

Odour Control

To remove odours, you need a carbon filter. And not just any carbon filter - one that’s deep enough for all air passing through it to be in to be in contact with the carbon for 0.1 – 0.2 seconds.

The trick is to match your carbon filter to yout extractor fan. To take the headache out of this, you can buy a complete extraction kit:

Don’t forget to change your carbon filter every 6 – 18 months, depending on the brand and type of filter.


CarboAir Filters CarboAir Filters

Choosing a Heater

Palma Grow Room Heater Palma Grow Room Heater

Most air conditioning systems will also heat your grow room. If yours does, you won’t need a heater.

If you do need a heater, choose one with an internal thermostat.

The heater will only warm when it needs to – all you need to do is set your target temperature.

There’s no worry of over heating or under heating…you don’t need to faff around with a timer. Best of all, your grow room will always be close to your target temperature.

KlimaHeat Electric Grow Room Heater promises to keep your grow room within 2°C of your target!

CO2 Equipment

For up to 40% more growth, aim for a CO2 level of around 800ppm (veg) or 1200ppm (flowering).

If you're really serious about CO2, you need either a closed loop setup or to run air cooled lights. Otherwise you'll end up just extracting loads of the CO2 you dose in.

To boost CO2 levels, you can:

Use a CO2 Generator

They’ll give you a consistent and perfectly controlled level of CO2, use a CO2 generator  with a CO2 controllerregulator.


Use MyCO2 Bags

One MYCO2 Bags will supply a 1.2m x 1.2m area with 800ppm of CO2 for 180 days (Grow) or 1200ppm of CO2 for 60 days (Bloom).

Unlike most CO2 bags, these ones don't produce CO2 until they're activated by you, so no CO2 is lost in transport or storage.

Air Circulation Fans

DiffuseAir DiffuseAir

Air circulation fans make sure that heat, humidity and CO2 are evenly distributed across your growing area.

Make sure you don’t point them directly at plants, this can cause too much water loss from the leaves, leading to windburn.

You can't go wrong with a DiffuseAir. They were designed to prevent harsh air streams that cause windburn. Unlike pedestal fans, they don't take up any floor space.

For spot cooling in areas that are tough to reach, use supplemental clip on fans. You can get them for as little as £9.95 each.

Humidifiers And Dehumifiers

As plants transpire, they naturally release moisture into the surrounding air.

If you have an air exchange system

Your air exchange system draws humid air out, so you may not need to dehumidify.

You may need to humidify though, especially during vegetative growth when your target humidity is 65 – 75%.

If you have a closed loop set up

You won’t be removing any of the moisture created by your plants.

This means two things:

  • It’s unlikely that you will need a humidifier once the plants have formed enough foliage.
  • You will definitely need a dehumidifier (or an air con system that deals with humidity)
Humidifier Humidifier

It doesn't have to cost a lot to manage your humidity. You can get a basic humidifier for as little as £59.95 and a humidity meter for only £9.95.

We recommend using the Dessicant Dehumidifier and Professional Humidifier.

For absolute control of your humidity, use a humidity controller. The GSE Humidifier - Dehumidifier Controller is a good option. 

ALWAYS Use an RO Filter with a Humidifier

If you don’t, mineral deposits will ruin your reflectors and reduce output from lamps. They’ll also clog up your carbon filters causing less extraction!

As a result, your equipment will need replacing more often. Worse yet, the resulting loss in light will severely impact plant growth. Find out more here.

Visit Your Local Store

For more advice, or to see some climate control in action, visit your local store.

If you’re thinking of creating a closed loop grow room, see how we’ve created ours in ColeshillBristolSheffield & Wembley!

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About the author

Tim started out in Dudley but is now the manager at Bristol! Drop by and you'll probably see him there.  

GroWell Hydroponics Bristol

Call GroWell Bristol
0117 955 8404