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[Hot Weather Alert!!] Easy Ways to Beat the Heat

[Hot Weather Alert!!] Easy Ways to Beat the Heat

27 Jul 2018

It's that time of year again. Temperatures spike and grow rooms overheat. If your grow room's getting too hot, here's what you can do.

1. Grow Lights

Your lights kick out the most heat in your grow room. Unless you want to cook your plants, follow these tips:

Run Lights At Night

Run lights at night Run lights at night

This is the coolest time of day! Since fans don't have to work as hard, running costs should drop.

Swap to cooler lights

LED Grow Light LED Grow Light

Lots of growers like switching to LED lights or CDM lights in summer - we ran a test and found your room will run a few degrees lower by doing this.

If you don't want to swap out your HIDs, use an air-cooled light (like the DARKSTAR). 

Keep Ballasts Outside

Raise Lights Raise Lights

Keep them (and the heat they produce) outside your grow room. 

Use a dimmable ballast

Digital Ballasts Digital Ballasts

Dimmable ballasts are digital. Digital ballasts already emit less heat than magnetic ones running at full power. To reduce heat output further, they'll dim lights right down to 250W.

Raise Lights

Raise Lights Raise Lights

Lights are a big source of heat - raise them up and away from your canopy if your grow room gets too hot. 

Remove a Light

Digital Ballasts Digital Ballasts

If worse comes to worst, remove a light! Don't forget, you'll need a LightRail to increase coverage from remaining lights.

2. Ventilation

The obvious thing to do is to extract more air. You can also:

Use A Speed Controller

Fan Speed Controller Fan Speed Controller

With a speed controlller, fans will automatically speed up when your grow room needs cooling. 

Be aware of intake air

Intake Air Intake Air

If the air outside your grow room is hotter than the air in it, first make sure you're drawing air in from the coolest place inside your property. If nowhere is cool enough, you might need to switch intake fans off.  Otherwise you'll just be heating your grow room further. 

Replace Carbon Filters

Replace Carbon Filters Replace Carbon Filters

Replace your 
carbon filter at the start of summer so pressure drop is at its lowest. At the very least, replace the carbon filter sleeve to reduce dust build up resistance.

Straighten Ducting

straighten ducting straighten ducting

This streamlines your airflow. Make sure you use metal bends rather than depending on twisted ducting

Overspec fans

Overspec Fans Overspec Fans

Buy a fan that's more powerful than you need it to be. Then in summer, you've got room to speed it up when you need to. In winter doing this should reduce running costs if you use an EC Controlller or Control Freak as fans don't have to work as hard to cool your room.

Target hot appliances

Target Hot Appliances Target Hot Appliances

A small Black Orchid fan will suck hot air away. Even if the appliance is outside your tent, you still want to cool it, otherwise you'll be warming intake air. If the appliance is in your tent, duct any hot air through a carbon filter. If it's outside your tent, duct straight out of your window.

3. Circulator Fans

To help stop hot microclimates forming, use air circulator fans

Cool appliances

Cool appliances Cool appliances

Point them at anything that gets hot - like chillers, lights, ballasts.  Even if the appliance is outside your tent, it'll still be warming intake air - make sure you cool it. If circulator fans aren't cooling it enough, use an inline fan to duct air through a carbon filter or out of a window. 


Aim them at corners

Aim them at corners Aim them at corners

Some of our low profile options will help you get at nooks, crannies and corners. Otherwise they'll become very hot and humid - a breeding ground for mould. 

Avoid your canopy

Avoid your Canopy Avoid your Canopy

If you point them directly at the tops of leaves you can cause windburn. The DiffuseAir is great for preventing this. 

4. CO2 Levels

Remember how photosynthesis works?

Light + CO2 + Water = Energy

If plants have the light and water but not the CO2, they can become stressed. 

humidifier humidifier

Add CO2 to ensure photosynthesis can continue at a really high rate. This'll increase growth and help plants cope with high heats of up to 29oC - 30oC. 

The best bit is that high temperatures actually improve CO2 absorption - it's a win all round. 

MyCO2 Bags are a great option. They're activated by you so won't release any CO2 until they're in your grow room. 

5. Humidity Control

humidifier humidifier

As your temperature goes up, so should your humidity. A higher humidity helps:

  • Prevent over transpiration (where plants lose too much water through leaves)

  • Bring your temperature down (2 - 3oC avg)

  • Keeps the stomata on leaves open (great for photosynthesis, which relieves heat stress)

  • Slow rate of pests breeding  

If using an RAM Humidifier, you can fill it with ice cubes of freezing cold water to help reduce temperatures. If using a Professional Humidifier, fill it with ice packs or big ice chunks. You'll need to top up your humidifiers 1 or 2 times a day.

6. Nutrient Solutions

In summer, you need to really keep a close eye on your feed - especially if you have a hydro system where roots are naked and exposed.

Use a Chiller

chiller chiller

The easiest way to keep your nutrient cool (18oC - 21oC) is with a nutrient chiller. It acts as a mini refrigerator.

Check It More Often

Check your nutrient Check your nutrient

In summer, as plants use more water, your feed becomes too concentrated, which can cause overfertilisation. 

Keep a close eye on your pH & CF.  If your feed becomes too concentrated, add some water.

Use VitaLink Chill

VitaLink Chill VitaLink Chill

Use it from the start of your grow and plants build up a heat resistance. It'll help plants prosper in conditions up to 40oC!

Other boosters & additives, like SHOGUN Sumo Active Boost and SHOGUN Silicon also help reduce heat stress. 

Use Silver Bullet Roots

Silver Bullet Roots Silver Bullet Roots

If your nutrient temperature becomes too warm, root diseases can take hold. To kill 99.99% of root diseases, add Silver Bullet Roots to your tank. A small dose with every tank change is all you need.

Grab some Iceline

Use Iceline Use Iceline

Another quick win is Iceline Pipe, which can reduce your nurient temperature by 3oC - 8oC. 

Cover tanks and pots

NFT Chilli Monster NFT Chilli Monster

To stop your feed being warmed by lights, cover your tank and pots. The Correx cover you get with NFT systems is great for this. Otherwise, use reflective sheeting (shiny side  up)! 

Use Silicon

Silicon Silicon

Silicon additives thicken stems, leaves & branche to lock in water. As a result, plants are better able to cope with climate extremes. SHOGUN Silicon and Emerald Harvest Sturdy Stalk are both silicon additives.

Biobizz Leaf Coat isn't a Silicon, but works in a similar wat. It coats leaves in a latex layer that helps prevent water loss

Use Sumo Active Boost

Silicon Silicon

Both Sumo Boost and Sumo Active Boost both help relieve heat stress when used as a foliar spray

Use SmartZen

Silicon Silicon

All SHOGUN Base Nutrients contain SmartZen. It's an exclusive additive that helps plants cope with heat stress by reducing the rate of transpiration

7. Propagators

The main problems you get in propagators during summer are caused by your temperature or humidity.


Propagator Temperature Propagator Temperature

Temperatures over 27oC will start to cause issues.

To keep your propagator cool, don't overdo it with your lights. Raise your light height if you need to. You can use ice packs to cool your nutrient solution in an Aeroponic Propagator

If using a heated propagator, think of putting it on a timer. 


Humidity Humidity

Too much moisture is a big cause of failed rooting. Aim for a humidity of 70% - 85% RH and make sure:

  • Rooting cubes aren't too wet

  • No water or solution is in the propagator tray

  • Only a light mist of moisture is visible on the propagator lid (no droplets!)

Water Level

chiller chiller

Don't forget to make sure there's always enough nutrient solution or water in your propagator. 

8. Bugs

During summer, pests breed quickly! And they love the dry and hot conditions in your grow room - especially spider mites. 

You don't need to do anything drastic. A lot of it is just common sense - like preventing cross-contamination and checking plants.

Be on the lookout

spider mites spider mites

Scout for pests more often - every 3-5 days should do the trick.

Take Preventative Action

spider mites spider mites


  • Use Spider Mite Predator Sachets 

  • Attach Bug Blockers to intake ducting

  • Never draw air in from outdoors

  • Don't use anything from someone else's grow room

  • Sterilise your grow room between crops

  • Use a humidifier to slow pest growth

  • Point oscillating fans at rootzones to slow Fungus Gnats right down

Leave your light running with your extraction off for a couple of days after finishing a crop. This'll send pests scurrying out your grow room!

9. Tent Size

If you're really struggling, try a taller tent.

The standard tent size is 200cm tall, but you can easily get a 215cm in your home. That extra 15cm of headroom will really make a difference.

About the author

Paul is our Merton shop manager. If you haven't met him yet, he's as friendly as they get. 

GroWell Hydroponics Merton

Call GroWell Merton:
020 8648 6327