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How to Control Humidity in Your Grow Tent

Last updated: May 4, 2020

control humidity in tent 2

Using a grow tent as a tool for housing a growing cannabis plant is a perfectly reasonable idea. Setting up an entire room to be suitable for a plant can be a huge hassle and not really worth it for a small grow-op.

However, since a grow tent is a much more enclosed environment than an open room, there can be a few issues that crop up. Chief among them is the question of how to control humidity.

Cannabis plants perspire all but 3% of the water they collect. If this goes uncontrolled it can lead to growth issues or molds ruining the plants. Thus, there are a few considerations to take into account when acclimating a grow tent for cannabis.

Air Circulation

Ventilation Fan-Vivosun-Amazon

Image: Ventilation Fan/Vivosun, Amazon

A big must-have for any grow tent is proper air circulation, for a couple of reasons.

Hot air always rises upwards, even with humid water molecules attached. This leaves our CO2 sinking to the bottom of the grow tent, underneath the plant canopy, where it can’t be utilized.

Fans are the obvious solution here. A common mistake is to use small oscillating fans at the top or sides of the room, but those don’t do a good job blowing through the plant canopy and stirring up the CO2 at the bottom.

Floor fans are ideal for this. They circulate the air, helping to dry things out and bring that useful CO2 up towards the plant canopy. However, they are only part of this equation.

Ventilation

grow tent ventilation-iPower-Amazon

Image: Grow Tent Ventilation/iPower, Amazon

Once the basic air circulation is figured out, the next step is to look at how overly humid air can escape the grow tent.

Luckily, there are plenty of exhaust systems available exactly for this purpose. These work by exhaling stale, humid air out of the grow tent through an exhaust vent while bringing new air in through an intake, ideally at the bottom of the tent.

As the exhaust fan blows air out, new air comes in through an open intake port in the tent. Repeat as often as needed for humidity to get to an ideal level.

Growers can program many models of exhaust fans to the only turn on if the humidity hits a certain level or on a simple timer. Other options include carbon scrubbers on the exhaust to counter any pesky odors. This also helps with controlling temperature, though alternatives may be needed for particularly warm or cold tents.

Air Conditioning

portable air conditioner-Whynter-ARC14S-Amazon

Image: Portable Air Conditioner/Whynter/ARC-14S, Amazon

Depending on the lighting system used in the grow tent, things can get pretty hot in it pretty quickly. It’s basically a small sauna in there under certain circumstances.

Portable air conditioners are the best option here, though the size needed is going to vary a lot depending on how big the grow tent is. A properly sized AC unit will handle temperatures just fine, and also help to get a fair amount of water from the air.

The important thing to remember is that cannabis plants like consistent temperatures. Keeping their environment fairly moderate, in the 70F-80°F range, and consistency is one of the best ways to improve yields.

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Dehumidifiers

Mini dehumidifier-Pro Breeze-Amazon

Image: Mini dehumidifier/Pro Breeze, Amazon

In most small to medium grows AC, air circulation, and a quality exhaust system should be more than enough to ensure a grow tent’s humidity stays within manageable levels. However, this is not always the case, especially when things go wrong.

Residential humidifiers will not do the trick here alone. They fill up much too quickly and are just not built to handle the massive amounts of water your cannabis plants transpire. The option of grabbing an industrial scale dehumidifier is also not really an option for most growers based on price alone.

This is why a lot of setups tend to forgo a humidifier in lieu of proper climate control and ventilation. However, this is actually not a great idea, either.

Humidifiers alone may not be the greatest option, but using one in tandem with other systems is one the best ways to make sure a grow tent stays at the exact humidity wanted. Depending on the size of the tent, most portable dehumidifiers will work just fine as long as they are being used alongside other tools.

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A Message on Insulation

None of the aforementioned humidity control options will work without a properly insulated tent.

When adding modifications, such as exhausts or intakes, precaution should be taken to ensure that any holes are sized properly for the tubing being used. A leaky grow tent can and will cause issues with humidity levels

Gaping holes in the side of the tent aside, a well-built grow tent shouldn’t have any trouble letting your tools do the work they were designed for.