Learn How to Efficiently Cool a Grow Room

How to Efficiently Cool a Grow Room

As we all know, various environmental circumstances such as in lighting, hydration, air purity, humidity, and many other factors have a significant effect on the growth of plants. Having a grow tent or room is one effective solution to breed cultivars under carefully curated conditions. 

Temperature is one element bearing a major impact on the conduciveness of a grow tent. Depending on the plant’s current stage of development, the appropriate ambient room temperature varies accordingly. Too much heat or coolness can impair the pace of growth and increase the susceptibility of plants to diseases.

In order to keep your cultivars at its ideal health, it is best to learn how to determine what your plant needs at every given moment. In this article, we will help you understand the basics of thermoregulation in a grow tent. So, let’s dive in.

What is the optimum room temperature in a grow tent?

To start with the basics, let us learn first what is the optimal room temperature in a grow room according to the different stages of the plant’s growth.

Fundamentally, the ideal temperature varies from one plant species to another. Some are thermophilic while other breeds favor a colder habitat. Although generally, plants thrive well in an environment with a temperature between 70° up to 80° Fahrenheit or equivalent to 20° to 30° Celcius. 

The range mentioned is well suitable during the vegetative stage. Young cultivars in this phase tend to grow best in a slightly warmer temperature with mid to high humidity. At night, however, modestly lowering the temperature without going beyond the suggested range may also help to promote faster and healthier growth of the crops.

On the other hand, plants undergoing a flowering or fruiting stage consistently require a slightly cooler environment, preferably around 65° up to 80°F or 18° up to 26° in Celcius. The act of lowering temperature aids in producing the best bud quality in terms of its density, color, scent, and trichomes. Moreover, it also beneficial to maintain a difference of 10°F or 8°C between the daytime and nighttime temperature to amp up the color development of the bud.

Life Stage Temperature Humidity
Cloning Stage 70°F up to  85°F High 
Seedling & Vegetative Stage 70°F up to  85°F Mid to high
Flowering or Fruiting Stage 65°F up to 80°F Mid to low

What are the consequences of an improperly set temperature in a grow room?

While it is ideal to maintain a fairly cool environment inside the grow room, there can also be hazards when you expose the cultivars to extreme temperatures. The table below shows the different scenarios that might occur between a space that is too cold or too hot for the plants to grow in.

Too Cold

(Less than 60°F or 15°C)

Too Hot

(More than 80°F or 26°C)

  • It can cause shock or lead to the death of Cannabis plants.
  • It has a relatively slower growth rate.
  • Produces minimal yield.
  • Susceptible to molds especially after the frosts have melted.
  • The leaves have a tendency to become too purple.
  • It has a much slower growth rate.
  • The buds tend to become loose and airy.
  • The plant’s potency and aroma may lessen.
  • Prone to fungal infections and other plant diseases.
  • It has a tendency to rot or wilt easily.

How does temperature affect different aspects of plant growth?

  • Relative Humidity 

Humidity plays an important role in facilitating the plant’s growth and the amount it yields as it determines its ability to absorb moisture. Humidity that is too high causes the leaves to reach in for moisture in the surrounding air. As a consequence, it delays the growth of the plant and increases its susceptibility to molds and as well as potential rotting of the bud. 

The other way around, an environment that has too low humidity prompts the plant to draw in much more moisture from the root. In effect, it causes stress on the leaves and may concurrently decelerate the growth too.

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The varying levels of humidity affect how much water the plant absorbs. Regulating the humidity in a grow room will give you better control over its nutrient intake and its resistance against diseases. The table below shows the ideal relative humidity at different stages of the plant’s growth.

Growth Stage Ideal Relative Humidity
Cloning Stage 70% 
Vegetative Stage 40% up to 60%
Flowering Stage 40% up to 50%
Final Weeks of Flowering Stage 40% up to 45%
  • Drying/Curing Process

A controlled level of temperature and humidity is also vital in the drying and curing stage of the newly harvested buds, especially in the case of marijuana. This process helps to bring out the aroma and improve the potency of the plant. 

Maintaining an optimal room temperature of 70°F or 21°C, the ideal humidity during the drying phase is set at 50%. Meanwhile, an RH of around 58% up to 65% is required for curing to take place effectively inside the jar.

Temperature Humidity
Drying 70°F or


50% RH
Curing (in Jar) 58 – 65% RH
  • Plant Color

In cultivating cannabis, various strains of marijuana can grow buds and leaves in colors pink, red, orange, purple or blue. Although the pigment is pre-determined by the plant’s own genetic makeup, the temperature can assist in either highlighting or suppressing its natural shade.

  • Growth Pattern

Temperature also affects the speed of the plant’s growth. In the case of cannabis, the plant tends to favor a slightly lower temperature during the nighttime. Consistently maintaining the coolness helps to make it grow faster. On the contrary, exposing it often to warmer temperatures at night might cause stunting or slowing of its upward growth.

How to cool down the temperature in the grow room

How to cool down the temperature in the grow room?

Now that we already know the baseline figures for the most conducive room temperatures and its probable adverse effects on the different aspects of the plant’s growth, let us then get into the various ways we can effectively cool down the temperature inside the grow room.

  • Air Circulation

Keeping the room with proper airflow is one essential factor to consider especially during the construction of the grow room or tent. The sizes and quantity of the fans to be installed must be relative to the size of the space in order to ensure it is sufficient enough to cover the entire area. Remember though to aim the blowing of the fans indirectly, like towards the wall or in constant rotation, so as to not enforce too much breeze against the plants.

  • Exhaust System

There are two important functions of the exhaust system in your space. First, it facilitates drawing the warm air out of the room and second, it helps to promote better air circulation. Both are equally essential in thermoregulation and in promoting a conducive environment for optimal plant growth.

  • Air Conditioning

Procuring a proportionately-sized air conditioner is one obvious way to guarantee the delivery of cool air into the room. Thus, it is perfect to use for really hot weather like during the summer season. Furthermore, ACs also help to counteract the heat emitted from the light bulbs and other various equipment such as pumps and generators. 

  • Type of Lighting

There are actually different types of lighting systems commonly used in a grow space. 

In the Air-cooled lighting system, it utilizes an extraction fan to blow air towards the bulb and expels it through an insulated ducting. In effect, the light bulb gets cooled while the warm air from it is drawn out of the space.

Alternatively, the Water-cooled lighting system uses a reservoir, water pump, and in some cases, a chiller, to cool down the lamp bulb. It is known to be more effective than an air-cooled mechanism and at the same time, it reduces the need for air conditioning too.

Another type of lighting used nowadays is the Light Emitting Diode or LED bulbs. This variety is least likely to emit heat, that is why it is great to use during the hot summer days. However, it may also come as a disadvantage during the winter season since it is not capable of producing enough heat to help warm the room. 

  • Lighting Schedule

Apart from choosing the appropriate type of light bulb, it is also necessary to strategically plan out its usage depending on the time of the day. So let’s say for example, during the vegetative stage, the plant requires at least 18 hours of light exposure. Given the condition, you can opt to light it from the very start of the day, then turn down the lighting for a duration of 6 hours during the midday wherein the environmental temperature is at its hottest. Thereafter, resume the lighting once again to complete the number of hours required. 

Setting the timer to shut off the lights at the warmest part of the day helps to eliminate additional heat into the room while still maintaining the desired level of temperature. Hence, subsequently requiring less effort and energy to cool down space. Furthermore, it also gives growers the chance to boost their savings.

  • Light Movers

We have already established that lighting is essential in the growth of the plants however it also contributes heat. Hence, using light movers allow the growers to spread the heat more uniformly across the area. In that way, it prevents the formation of hotspots, more so extend the distribution of light even to the usually shaded parts of the room.

  • Room Insulation

Installing a foam insulation in your grow room helps to keep the space cool by acting as a barrier to prevent the outdoor heat from penetrating inside. This is particularly advantageous if the room or tent is widely exposed to sunlight or with minimal shade only surrounding the vicinity. 

  • Cooling Humidifiers

With proper usage, the cooling humidifier is a helpful tool to keep the temperature cool and simultaneously provide moisture to plants. It works by spraying fine mists of water sourced out from a designated tank. When using this device, however, you must always monitor the level of relative humidity since too much moisture can also have an adverse effect on the health of the plants.

  • Reservoir Placement & Chillers

Naturally, soil provides the cultivars better protection against temperature fluctuations. Hence, in the case of the plants cultivated above the ground, they are inevitably more vulnerable to overheating of roots. To avoid that from happening, it is highly advisable to position your reservoir in a cool location to prevent the contents from warming.

If moving the placement of your reservoir least likely possible or inconvenient, then putting a bottle of frozen water in the nutrient tank can be an excellent quick fix. However, for a more stable and consistent solution, it is best to invest in a reservoir chiller instead. This will ensure that the nutrient solution is at its favorable temperature to effectively keep the plants cool and inhibit the growth of harmful bacteria, molds, and mildew.

  • Smart Pots

Smart pots primarily are plant containers made out of heavy-duty fabric that provides the roots with better aeration and drainage. Since the pot allows air to flow through, the risk of overheating is efficiently minimized resulting in an enhanced health and growth of the cultivars.

On  a side note, placing the plants in smart pots is simply not enough. It is also equally important to consider the appropriate quantity of pots the grow room can accommodate. Overcrowding is one common mistake that contributes to untoward warming of the space.

Read Also: Easy DIY Carbon Filter for A Grow Room

The tips shared above are just a few of the basic solutions commonly available to facilitate the cooling of your grow room. Not only will this promote better health for your plants but it can also conceivably increase your total yield. They are simple and mostly inexpensive to implement thus it is worthwhile to give each one a try.

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