Humidity & Temperature Control

Humidity & Temperature Control


Controlling your temperature and humidity levels in your grow space is a very important aspect of indoor cannabis growing. Whether you have already set up your grow space or are still in the planning stages, you should consider investing in the proper tools that will ensure your plants are at their optimum health. In this guide we will go over all the aspects of controlling your temperature and humidity as well as discuss a few products that can benefit you as a grower.


Optimal Conditions for Optimal Cannabis

To successfully cultivate cannabis indoors, you will need to know the best growing conditions for the plant. While it’s true that every strain has slightly different needs, the overall environmental requirements are more or less the same. Below we will take a more in depth look at the exact temperature and humidity levels that cannabis tends to thrive at.


The ideal temperature range for cannabis is generally between 68 and 77°F (20 and 25°C). As your grow space makes the transition between ‘day’ and ‘night’, try not to let there be more than an 18 degree difference between the two temperatures. Some growers prefer temperatures higher than the recommended range as it generally stimulates the cannabis to grow faster. However, this can stress the plants and also requires increased levels of watering and potentially more added nutrients. Oftentimes it is recommended as a general rule of thumb to keep the temperature towards the higher end of the range while the cannabis is vegetating. Then once the plants move to their flowering stage, lower the temperature to the cooler end of the range.


Humidity, often referred to as relative humidity, is the percentage of moisture in the air. For the most part, cannabis tends to prefer the humidity level somewhere between 40 and 70 percent. Similar to temperature, vegetating cannabis likes the higher end of the humidity range and flowering cannabis prefers the lower end.


For example, sprouting seeds and seedlings prefer upwards of 70 percent humidity. This allows their root system to have ample access to nutrients in the grow medium and encourages the plant to grow stronger. As the plants fully enter the vegetative stage you can decrease the humidity level slightly.


Gradually lower the level until the cannabis reaches its flowering stage. At this point, the humidity should be somewhere between 40 and 50 percent. As you get ready to harvest the buds, you can drop the humidity even lower to somewhere between 30 and 40 percent. Remember, do not go lower than 30 percent humidity as this can cause your plants to go dormant.

Carbon Dioxide

Another important aspect in your environment for your cannabis is the CO2 or carbon dioxide levels. This is more or less controlled by the amount of fresh air available to your plants. By using a simple accessory like a fan, the air will be circulated enough that your plants have ample CO2 access. Thankfully there are tools that measure CO2 levels in addition to other factors like humidity and temperature that can make your life easer.

How to Control Temperature and Humidity in Your Grow Space

Depending on the size of your grow space, it may change the way you will control the temperature and humidity levels. For example, a well insulated room as well as a good quality grow tent will both maintain optimum temperature and humidity levels easier. Also, depending on the equipment you already have in your setup, your needs may change.


For examples, lights like HIDs consume high amounts of electricity and put off large amounts of heat. This can cause temperature to spike so you would need fans to ventilate and make sure the temperature doesn’t go too high. On the other hand, if you use LED lights which put off little to no heat and your space has thin or zero insulation, you may need to use something to heat the space instead. All of these factors can determine your exact humidity and temperature needs. Below you can find information on basic tools and accessories to make monitoring both environmental factors easier as well as information on individual products to meet your unique growing needs.


How to Choose the Best Tools for Your Setup

When it comes to choosing the best tools for your cannabis growing needs, there are several factors to take into consideration. First, you should take a look at how many plants you currently have as well as think about how many you eventually want. This can factor into the size of some of your equipment as well as perhaps buying equipment that syncs well with other components if you need to expand.


You’ll also want to make sure your grow space is as cost effective as possible. This means choosing more energy efficient lights like LEDs over HIDs. While sometimes this means a larger initial investment, you’re really saving yourself money in the long run. Investing in all of the equipment to make your setup and grow space perfect for your cannabis plants will benefit you greatly as a grower.


Also make sure you know whether or not your cultivation of cannabis is legal in your state or area. If it’s not, you’ll need to take necessary precautions in equipment like monitoring your electricity consumption and making sure the space is well-ventilated. In some cases, a carbon filter to eliminate the cannabis odor can be a great investment. An ionizer can also be used to neutralize the odor immediately should the need arise.

Tools to Measure Humidity and Temperature

At the very least, you will want a hygrometer and thermometer. In many cases, you can find a tool that performs both functions. These are usually referred to as thermo-hygrometers. It’s always advisable to treat these tools as investments that will help your production and/or business in the long run. For this reason, you should buy the best quality products that are within your budget so you don’t end up having to purchase new supplies two or three years down the road.


Here are a couple of great thermo-hygrometers that are sure to meet your needs.

Extech 445713 Indoor/Outdoor Thermo-Hygrometer

This product is great for growers who want a basic digital thermo-hygrometer. It has big display numbers which make the meter easy to read. This meter measures both indoor and outdoor temperature and humidity at the same time with clear readings for both. The unit can be mounted on a wall or other similar surface for easy reading. This makes it easy to monitor environmental conditions with the meter out of the way.

The temperature display can read in either Fahrenheit or Celsius and ranges from 14 to 140°F (-10 to 60°C). The temperature is accurate down to 1.8°F. The humidity sensor ranges from 10 to 99 percent relative humidity or RH. The meter has a dual display so both the indoor and outdoor conditions read simultaneously. This meter also records highs and lows which can be seen by using the MAX/MIN button. This is a great feature to really make sure your environment for your cannabis is the best it can be.

Ambient Weather WS-08-X2 Wireless Indoor/Outdoor 8-Channel Thermo-Hygrometer

This handy wireless thermo-hygrometer is perfect for anyone who prefers a cord-free work environment and grow space. It is incredibly easy to use and is compatible with up to seven additional meters. Depending on the monitor package, you can customize the number of consoles and individual sensors or remotes you buy. This allows the customer to really have control over their purchase and as a grower, you’re able to cater to your own cannabis’ needs better.

The console itself displays temperature and humidity as well as minimum/maximum temperature and humidity. The temperature can be displayed in both Fahrenheit and Celsius. If you have more than one remote or sensor set up, you can use the scroll mode. The scroll mode allows you to see data from all of the sensors without actually manually pressing any buttons. Each channel will simply display for five seconds. Also important to note, the sensors all work both indoors and outdoors.

Tools to Measure Humidity/Temperature/CO2/etc.

If you prefer, you can even buy tools that display multiple environmental factors beyond just temperature and humidity. These tools are predominantly useful for measuring temperature, humidity as well as CO2 levels, all important components in a healthy grow space. Some of these tools also can control lighting and watering as well.

Here are a couple of these handy multifaceted tools.

CO2Meter AZ-0004 Indoor CO2 Meter, Temperature and Relative Humidity

This all-in-one tool provides you with accurate readings about several aspects of the air quality in your grow space. The meter measures CO2 levels, temperature as well as relative humidity levels. The tool is self-calibrating and has no moving parts. The machine is very easy to use, simply plug it in and it will get to work.

The reading ranges are as follows:

  • CO2: 0-10,000ppm
  • Temperature: 0-120ºF (-18-49ºC)
  • Relative Humidity: 20-99.9% RH

Hydrofarm Autopilot Desktop CO2 Monitor & Data Logger

Hydrofarm is a popular brand in the cannabis industry as they produce nearly all needed equipment to set up a grow space. The display reads CO2, temperature and relative humidity levels. The machine includes an audible alarm for both low and high levels of CO2, as both can be detrimental to you and your plants’ health. This device is easily portable to different areas of your grow space or to move from one grow space to the next. You can also power this machine with a USB as well such as from a laptop or external battery pack.

Tools to Heat Your Grow Space

For those grow spaces that tend to be on the cooler end of the temperature spectrum, here are a couple of space heaters that can help.

Honeywell HCE840B Heat Genius Ceramic Heater

This heater is great because it is affordable and also sleek so it can fit nearly anywhere in your grow space. The heater features six different heat settings, which helps you to really customize your setup. Honeywell states that because of the six heat settings, the heater is suitable for both large and small spaces. This makes it a viable option for all levels of growers.

The Heat Genius also features several safety features to give you greater peace of mind when you have to leave your grow space. It can be programmed with a timer as well as programmed to start at whatever temperature you desire. There is also a quiet mode in which the heater is on a low heat setting and fan speed, helping the surrounding environment remain more relaxing.

Lasko 754200 Ceramic Heater

This heater is great for growers with smaller spaces. It’s listed as being suitable for small spaces like desk tops, so it could be potentially used in a grow tent. However constant supervision would be required in that case. The 754200 has three heat settings: high, low and fan only. Similar to the Heat Genius, there is a overheating safety measure in place.

The thermostat is customizable to your exact needs. This is great if your strain maybe needs a little less or more heat than other ones. The heater comes full assembled and even features a convenient carrying handle.

Tools to Cool Your Grow Space

On the other hand, if you have trouble with too high of temperatures, here are some products that will help you cool things down. Keep in mind that your inline fans that you most likely already have to circulate fresh air into your grow space will likely cool the space as well.

Honeywell MN12CES MN Series 12,000 BTU Portable Air Conditioner

This air conditioner also has a dehumidifier built into it as well. This tool can be very helpful for growers who are looking to maximize their investment efficiency and want to accomplish as much as possible with few accessories. The components can run separately or together.

The air conditioner can cool up to 450 square feet and the dehumidifier can collect up to 79.2 pints of water a day. The display feature LED lighting and touch controls. There is also a fully functional remote as well. In addition, users have a choice between three speeds. An on/off timer option also exists.

Woozoo HD18NU Whole Room Circulator Fan

This fan is great for those with a small grow space and who only need to lower the temperature slightly. If your inline fans aren’t doing the trick, use this fan to make sure the job gets done. The design is incredibly compact, which makes it effective in any sized grow space.

The fan has six vertical settings. This is helpful to direct the airflow to a specific area. Remember, you generally don’t ever want to place a fan, heater, etc., directly at your plants. As for speed, the user has the choice of three settings. The lowest speed is virtually silent, which allows for less noise pollution. This fan can cover up to 275 square feet.

Tools to Raise the Humidity in Your Grow Space

For cooler and temperate climates, humidity may be too low without assistance. As mentioned previously, different plant stages require different humidity levels. In addition, we talked about how it is important to never go below 30 percent relative humidity when growing cannabis.

If you’re natural environment does not meed these needs, then consider adding a humidifier to the mix. There are two types of humidifiers: warm and cool mist. Both of these types can also affect the temperature of your grow space, so keep that in mind as well. Here are a couple of great humidifiers than can help you reach optimum relative humidity levels.

VAVA Cool Mist Ultrasonic Humidifier

The VAVA Cool Miss Ultrasonic Humidifier is a convenient and space saving unit. Cool mist lessens the likelihood of the space temperature increasing too much. It fills from the top, simply lift the lid and add the water. This is great to prevent any spilling or leaks. The tank is 84.5 ounces or 2.5 liters. The design it self allows cleaning to be incredibly easy as well as there are no small places that can’t be reached.

The base is always cool to touch, so there is no risk of burn as the unit operatates. In addition, the base and tank are actually separate components, so mold will not grow. The nozzle rotates a full 360° which allows you to direct the moist air in any way you like.

There are three timer modes. These include ‘Auto-Start’, ‘Auto-Off’ and ‘Sleep Mode’. This allows the unit to really be personalized to your needs. The best part, you get all of these features at a very affordable price.

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