How to Control Your Temperatures in Summer?

Grow room temperatures in summer

Perfecting your environment can be a bit of a struggle when summer arrives. Many growers face elevated temperatures and inconsistent humidity ranges throughout the warmer months due to the warmer air and summer heat. With this in mind, it is essential that you have the equipment in place to manage this. If your plants are exposed to high temperatures, they will show visible signs of stress, and in most cases stop absorbing nutrients and mainly consume water. Throughout the flowering stage of the growth cycle, when relative humidity spikes, your plants are at risk of developing botrytis.

What is botrytis?

In simple terms, botrytis is a type of fungus that thrives in environments with high humidity. It will cause the flowers on your plant to rot, making all produce unsuitable for consumption. During the stages of vegetative growth, an increased humidity level will help accelerate growth across your crop.

So, what grow room temperatures should I aim for?

  • Temperature lights on – 24-28C
  • Temperature lights off – 22-24C
  • Humidity propagation – 70-80%
  • Humidity vegetative stage (18/6) – 65-75%
  • Humidity flower (12/12) – 40-65%

The first piece of equipment you will need is a Digital Series Thermometer/Hygrometer. This will provide you with accurate readings within your grow room. Once you have a better understanding of the temperature and humidity levels in your space, you will be able to learn how to control these more effectively.

Now you’ve got your thermometer/hygrometer, it’s time to look at your lights. If you are using HPS/HID lighting, you will have noticed that these run extremely hot when compared with LEDs. At London Grow, we strongly recommend using LED lights due to the highly effective heat dissipation and low heat output.


Digital Series Therm. / Hygro.


HPS Grow Light Kits


LED Grow Lights



What is an extraction kit?

An extraction kit simply refers to the combination of ducting such as aluduct, combiduct or sonoduct, a premium Rhino or GAS Carbo Air Carbon Filter, and an AC or EC extraction fan. Ensuring you have a top-class extraction system is one of the most important steps to reducing your temperature and preventing air from stagnating in your space.

At London Grow we strongly recommend opting for an EC fan as this will help reduce energy costs, as well as noise output, whilst still maintaining premium extraction capabilities. For best results, we recommend routing your ducting away from your grow room out of a window. This will ensure that the same hot air that you have just extracted from the space is unable to circulate back in.

Selecting your extraction kit will be dependent on the size of your grow room, as well as the type of lighting you use. The more lights, the bigger the fan! If opting for a dimmable fan, we recommend selecting a fan that overcompensates for the space you have. If you do this, you will have peace of mind that when the temperatures increase, you’ll be able to tackle these.


GAS CarboAir 50


RAM Carbon Filter


Rhino EC Ultra Silent Fan



How do I know which fan to use?

To work out the correct sized extraction fan for your space, you will need to use the below formula. We will use a 1.2 x 1.2 x 2.0 Lighthouse LITE as an example:

Step one

Simply multiply the L X W X H

1.2 x 1.2 x 2.0 = 2.88m3.

Step two

Multiply this figure by 60. You multiply this number by 60 as you need to calculate the air change per hour.

2.88m3 x 60 = 172.8m3

It’s important to note that when you couple your fan with your carbon filter, the efficiency of the fan will reduce by 20%. With this in mind, you should opt for a fan with an additional 20% power than needed for your space.

To streamline your environment, it’s worth considering opting for a controller such as the Enviro Controller. This will help automatically balance out your environment based on the temperature and humidity parameters you have set for both day and night.


GAS Enviro Controller


Rhino Hobby Carbon Filter


Rhino EC Ultra Fan



Do I need an intake fan?

If you are growing in a small space, you can achieve passive intake by opening the vents. As you will have negative pressure from your extraction kit, this will automatically pull in fresh air through the vents. For larger spaces and grow rooms, we recommend adding an intake fan. Generally, growers will opt for an intake fan that is one size down from the extraction fan. For example, if you are using a six inch extraction fan, you should use a four inch or five inch intake. Make sure that the intake is approximately 30% less powerful than the extraction.

For best results, at London Grow we recommend using a premium fan controller to balance your intake and outtake fans. If you opt for the Rhino Ultra Silent EC for extraction, and the Rhino Ultra EC for intake, you should go for the Rhino EC Smart Controller.

Air circulation

Now that you’ve got your extraction system set up, it’s time to look at circulation fans. In nature, plants are constantly exposed to wind which in turn helps strengthen the overall structure of the plant. Further to this, research has shown that increasing air flow can have a positive impact on the size of flower production, as well as the quantity. With this in mind, it is essential that you maximise air movement in your grow tent. VVIND Fans are top-quality 3 speed oscillating wall fans that are perfect for keeping air moving in your space. For those of you with smaller spaces, the Vortex Clip on fan is a great alternative.


VVIND Systems Wall Fan


Vortex 6" Clip on fan


Secret Jardin Monkey Fan



What about CO2?

Implementing carbon dioxide in your grow space enables you to increase the maximum temperature that your plants can be exposed to. If CO2 levels are raised to between 1200PPM and 1500PPM you can push your temperatures up to 29-35C. This is ideal during the summer months if you are having trouble controlling your temperatures. Typically, when your plants are in an environment of 35C you will notice they are visibly suffering, but not with CO2! If you opt for this method, you must make sure that you increase nutrients and watering in order to maintain healthy growth throughout all stages of the growth cycle. Not only will CO2 enable you to run your temperatures higher, it can also drastically increase growth rates throughout the vegetative phase of the growth cycle, which in turn can reduce the grow cycle by 1-2 weeks.


Airbomz Co2 Can


Exhale CO2 Bag


Smart Co2



In case of emergencies…

Sometimes we do experience periods of elevated temperatures, and these can cause a bit of panic. If you’re struggling to keep your grow room under control, we recommend keeping a bottle of ESSENTIALS No Stress on standby. Chill is a unique formula that protects your plants from periods of high heat, enabling them to thrive in conditions up to 32C. Another great additive for preparing your plants for dealing with high temperatures is Grow Genius Mono-Silicic Acid.


Grow Genius Mono Silicic




Biogreen X-Force



Grow room temperatures in winter

Throughout the colder months, outdoor temperatures will in most cases directly affect grow room temperatures. In order to bring your temperatures back to optimal range, you will have to take some extra steps to raise temperatures.

Increasing temperature

To raise the ambient temperature in your grow space, we strongly recommend opting for an oil filled radiator. These are better than the typical electric radiators as when the optimum temperature is reached, and the radiator turns off, the oil variant will still emit heat until it cools down completely. The electric radiators lose heat almost immediately.

Balancing temperature with other environmental factors

At London Grow we love the GAS Enviro Controller V2. This handy bit of kit allows you to control both intake and extraction fans, as well as having an extra two sockets that can be programmed to control whichever components you would like to add. For example, a heater and dehumidifier. The reason we opt for these is that both will help increase temperatures in your grow space.

Simply set your parameters and the controller will work hard to balance out each component effectively in order for you to maintain the perfect environment for your plants to thrive all year round.

Keep an eye on the positioning of your intake fan. If your intake fan is constantly bringing cold air into your grow room, you will find it significantly harder to maintain a constant temperature.

I still can’t get my temperatures up!

If you’ve already got a heater in your space, and you are still finding it hard to keep the plants within range, this is where you would consider switching your LED light fixtures for HPS. HPS lights emit massive amounts of heat which in turn will drastically increase the temperature in your grow space.


VitaLink Heat


GAS Enviro Controller


Lighthouse 3kW Heater



Just like for summer, you can use the same additive for Winter. ESSENTIALS PLUS No Stress helps your plants develop resistance to temperature drops. Once again, when adding No Stress to your reservoir, you must ensure that the nutrient solution is within the correct temperature range. If you go down this route, we recommend you use it only when absolutely necessary.




Grow environment