Unfortunately for the average indoor cultivator the summer season is the worst time to grow. With the rise in ambient temperature the inside of a grow room can reach and breach 30c…. this is the start of the danger zone for your plants where growth rates slow! If you are a grower who dreads every summer then we’ve got you covered, learn some useful tips about how to keep your grow room temperature under control. There are multiple ways to combat the rising heat so your grow can continue, and you can achieve at least some result instead of losing a crop or not even starting one. Below are several methods that are easy to implement and can shave you off a few degrees here and there, a few degrees might not sound like much, but it could be the difference you need to restore a suitable environment for your plants.

Extractor and Circulation Fans

Airflow is massively important for your tent or grow room, a well functioning ventilation system should change the whole volume of air every few minutes. As a very simple rule of thumb you should have approx 300-400m3 of extractor capability per 600 watt lamp, in addition to this calculations should be made to account for the ‘drag’ affect on a fan that is produced by attaching a carbon filter, ducting and fittings. Attaching a carbon filter to your ventilation system can reduce its capacity by as much as 30% and each fitting in a ventilation system will affect the extraction capabilities, also try to keep your ducting as simple as possible, maintaining short ‘runs’ of ducting where possible. A single fan can do the job in a small grow environment of drawing air in passively and extracting the hot unwanted air, however a better system would favour an intake fan, (typically approx 1/2 the power of your extractor fan, coupled with an ‘intelligent controller such as the control freak or G.A.S enviro controller) enabling the grower to maintain a desired temperature, this represents the best option for a simple ventilation system. If you are finding that the heat just can’t be controlled with what you have in terms of extraction then it is clear your extraction system is not up to the job and you should consider moving to larger intake and extract fans. In our experience
the investment made in a good ventilation system cannot be understated, one of our first questions to our customers experiencing problems is what type of ventilation system do you have? more often than not problems are down to poor environmental control. You will also need air circulation fans inside your grow room or tent to circulate fresh air from your intake fan evenly around your grow room. Circulation fans will also help stop any hotspots, keep them on whilst your lights are on, and for 15 minutes after the lights go out. Oscillating fans and clip on fans make it easy to reach all areas of your grow room or tent.

RVK Sileo 150E2 428m3/hr

Phresh Hyper Fan 150mm

Revolution Vector EC Fan 150mm (6″) 796m3/hr

Secret Jardin Monkey Fan Oscillating

Heavy Duty Pedestral Fan 18″

Adjustable Ballasts

An adjustable ballast enables you to reduce the lamp output and thus the heat output. Most adjustable ballasts have at least 3 settings to choose from. 250w, 400w and 600w. If you are approaching low to mid 30’s, then simply switch down to the next setting. Shaving 200 watts per ballast soon adds up and will still give you a worthwhile result. Now I should point out that if you have a 600w lamp attached and you switch down to 400w on the ballast then your lamp will no longer be at peak efficiency…..you should ideally match the lamp with the setting to keep your lamps firing at full efficiency. BUT……in times of emergency its not going to affect you that badly. So to simplify…turn the power down. Manufacturer such as Gavita are now are providing controllers for their own lighting systems that will automatically reduce the output of your lamps should an excessive temperature be reached in your grow room.

SolisTek 1000w Adjustable Digital Ballast

SolisTek 600w Adjustable Digital Ballast

Lumii Black 600w Digital Ballast 250w-660w


The efficiency of LED lighting is unsurpassed and also unbeatable when it comes to heat emission. LED’S provide a better quality of light in the Photosyntethically Active Radiation (PAR) spectrum over HID’s with the added bonus of less heat produced for the investment you have made in providing the right light levels. Our range of LED lighting is increasing due to demand and more and more people are switching over as LED’s as they require less ventilation in a grow room or tent compared to High Intensity Discharge lamps (HID). So it may be a consideration for you to upgrade your lighting system to LED’s if you are constantly struggling to maintain correct temperatures using HID lamps and ballasts.

LED hydroponics Grow Lights 

Air Cooled Lighting

Air cooled reflectors are connected to extraction fans, ducting fresh air from outside the grow environment through an air sealed reflector pushing hot air from the lamp and then ducting it to the outside of your grow environment. As most of the heat in a grow room using HID lamps is produced by the lamp using air cooled reflectors is a great way to reduce the overall heat in your grow room and make your environment more controllable generally. Cool tubes are slightly smaller than larger hoods and are great for single lamp set ups and better suited if there are space restrictions inside the tent.

Maxibright Goldstar Grow Light Reflector 150mm

CoolTube Reflector 150 x 400mm

Carbon Dioxide

CO2 in high enough levels can allow the plant to thrive in hotter conditions, however applying CO2 along with all the other variables needed for this type of ‘accelerated growth can be very expensive and in the end hit or miss. That said maintaining 1200-1500 PPM of CO2 in the grow area allows growers to keep temperatures much higher than normal (30c upwards) A full CO2 system can be expensive but very effective with the potential to increase normal yields by 30%. There is also a cheap and cheerful way to add CO2 to your grow room, the CO2 bag. Exhale make a CO2 bag that slow releases CO2 into the area it is in. Easy to use and a very simple way to negate major heat stress.

Co2 Exhale Bags XL

Air Conditioning and Chiller Units

The best way to control the heat is to use an air conditioning unit, correctly sized a good air conditioning unit will maintain correct temperatures very specifically. Great bits of equipment although they can be a little bulky and a little pricey. Hydroponic enthusiasts will benefit from water chillers. Keeping an NFT system reservoir below 20 degrees when the ambient temperature is 30 degrees can be a difficulty, save yourself the risk of root rot by getting a chiller. Simply plug it in and set the temperature at 18c. At least that’s one less thing to have to worry about. If you want to guarantee your summer temperatures, then get yourself one of these…

Tank Heaters & Nutrient Chillers

Horticultural Air-Conditioning

Nutrient Additives

There are a few things you can add to your tank to help with relieving heat stress. Seaweed and Kelp products are great Kelp naturally contains lots of trace elements and minerals that have protective properties for plants. Humic and Fulvic products, humic acids have protective abilities and can help plants deal with water stress and drought. Silicon offers additional support to plant cell walls. This helps your plants be more resistant to heat and other types of stress.

Silicon 250ml

Cyco – Silica 1ltr

Fish-Mix Power Fertiliser 500ml

Diamond Nectar 1ltr

Whatever your heat stress problem, we can fix it.