Last Updated on April 25, 2022 by Gary Stephen
As indoor growers, we are bound to recreate the likeness of the natural environment. Thus, it is expected of us to make some adjustments to mimic nature. This includes creating negative pressure across the grow tent. Doing such will help us achieve good quality and optimal yield in the end. But, how do we fix negative pressure inside the grow tent if it is too much?
In this article, we will discuss the basics of room pressure. We will also tackle why negative pressure is important. Moreover, how does this affect your plants and how to do it in the right way.
The basics of pressure
The pressure refers to an area of force. It can either be positive or negative. You can say that it is positive when the pressure inside an enclosed room is higher than the outside. In that case, the gas and liquid contained within are pushing the surface outward for release.
The negative pressure is the exact opposite of the scenario above. In this case, the pressure inside the room is lower than that of the outside area. In that condition, the gas and liquid are likely drawn inwards to fill the space within. Unlike in positive pressure where elements are pushing to escape.
Benefits of negative pressure in the grow tent
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Increases the yield.
A negative pressure room expels hot and humid air out of the grow area. Maintaining that stable environment provides you a better chance to increase your yield.
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Minimizes the formation of molds and mildew.
The continuous removal of excessive moisture from the grow tent prevents certain problems. These are diseases that arise from having too much humidity. It includes the formation of pesky molds and powdery mildew.
Molds and mildew are common and easy to treat once detected early. But if left unattended, it can ruin your entire harvest.
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Odor management.
Odor can be due to the aromatic nature of the plant itself or could also be because of the type of soil media used. Either way, a negative pressure room will help to remove the unwanted smell.
Through constant extraction, it inhibits the odorous air from lingering throughout the tent. Managing the unpleasant scent not only benefits your space. It would also spare you the complaints from your nearby neighbors.
How is negative pressure created in the grow tent?
The grow tent functions as an enclosed environment. Meanwhile, the ventilation system serves as the source of air. The rate of air supplied or discharged is what determines the pressure inside.
In building negative pressure, more air is likely expelled than taken in. So, it is logical to say that your extraction fan should be more powerful than your intake fan. It is either you use a bigger size or you can have several small extraction fans to increase the power. The release of more air lowers the pressure inside the room. Thus, establishing negative pressure as desired.
You can tell that you achieved negative pressure by the mere look of the shape of your grow tent. The structure would tend to appear a little bit concave and pulled in. It seems so because of the vacuum effect that it creates. The slight curvature implies that the pressure is still within tolerable limits.
Nonetheless, there is also a thin line between having enough from too much pressure. This can be easy to determine by examining the poles of the tent. Excessive pressure forces the poles to weaken and cause it to bend inwards. In that case, you have to immediately carry out measures to prevent the tent from collapsing.
How to fix too much negative pressure in the grow tent?
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Use of active air intake
Sometimes the mere airflow from vent holes is not enough to catch up with the amount of exhausted air. In effect, the negative pressure within the room is even further increased. Having said that, passive intake alone is less applicable when maintaining the negativeness.
Active intake ensures the forceful entry of air in the grow space. It uses an intake fan to aid the drawing in of air. Thus, it becomes more effective to cope up with the amount discharged. As a result, the regulation of negative pressure is being maintained at a suitable level.
The use of an intake fan will depend on the size of the grow tents. In normal settings, tent sizes 4×4 and below would not need the use of intake fans. Thus, they can get away using the simple passive air intake approach.
Nonetheless, for bigger or higher tent sizes, active air intake is much more necessary. Now, intake fans also come in different sizes. Depending on the dimensions of your tent, the CFM or cubic feet per meter also varies.
Here is also a quick list for your reference:
| Grow Tent Size | Intake Fan Size | Our Top Picks |
| 4×8 | 285 CFM | Lotus Analine 260 CFM Inline Duct Fan |
| 5×10 | 650 CFM | Can Fan 675 Mixed Flow Inline Fan
Hurricane HGC736585 780 CFM Commercial-Grade Inline Fan AC Infinity Cloudline S8 807 CFM Inline Duct Fan w/ Speed Controller |
| 8×8 | 906 CFM | iPower 1060 CFM Inline Duct Ventilation Fan |
| 10×10 | 1,600 CFM | Can Max Fan 1709 CFM Mixed Flow Inline Fan |
Then again, there are a lot of factors that come into play. CFM requirements would still differ depending on the prevailing conditions of your tent. To know more about how to calculate CFMs, please check this article. Grow Room Fan Size Calculator with Size-wise CFM.
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Make use of a fan speed controller
The fan sizes come with their own accurate calculations. Even so, you may not be able to find such an inline fan with the same exact CFM available in the market. Thus, this is where a fan speed controller becomes helpful.
The speed controller allows the growers to regulate the fan speed as needed. You can choose to decrease it if the fans CFM happens to be higher than the required. You may need to do some trial and error here until you find the right settings for your space.
Our top picks for fan speed controllers:
Yescom Variable Fan Speed Controller
Cdmall 350W Electronic Fan Speed Controller
AC Infinity Fan Speed Controller
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Light Proof your vent flaps.
One way to counter the negative pressure is to add more air intake. Luckily, some grow tents have built-in vent flaps at the bottom. Although the problem with extra holes or air passages is that they are not all light proof.
If your tent has this vent flaps, check if it is light proofed already. This is essential in preventing the disruption of the light/dark cycle of the plant. If your vent flaps are not yet light proofed, you can use the following techniques:
- Positioning the opening in the darkest side.
- Using layers of canvas.
- Or, using cloth duct tape.
- Using gaffers tape.
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Build an extra ducting for air intake.
Not all tents come with the same advanced design. Some brands don’t come with extra vent flaps at the bottom. This is not a problem though. If your tents don’t have it, then why not make it yourself.
Building extra ducting for air intake will aid in reducing the negative pressure in the room. To create even distribution, it is best to place this at the bottom. But then again, adding holes increases the chances of introducing unnecessary light exposure. As mentioned before, this may interrupt the light/dark cycles of the cultivars.
So, a simple DIY cardboard project may help to light proof the hole. You can use a cardboard box big enough to fit the space in your tent. Cut holes on its three sides. The bigger the passive ducts means more air can enter to counter the pressure.
We recommend using a 6-inch ducting for an area of 50 square feet or more. It is better to cut it long enough to form an S-shape. S-shapes are effective in keeping the light from penetrating the space.
Moreover, you can also bend the ducting at a 90-degree angle. This will further help to prevent light from getting through inside the grow tent.
Our top picks for 6 Inch ducting:
AC Infinity Flexible 6 Inch Aluminum Ducting
Hydro Crunch 6 Inch Lightproof Aluminum Ducting
Terra Bloom 6 Inch White Flexible Ducting
The bottom line, it takes more air extraction and less intake to create negative pressure. Maintaining that allows growers to gain better control over the grow tent environment. It makes it easier to regulate elements including temperature, humidity, and CO2 levels. As a result, it ensures the production of good quality yield. In the end, it makes all the slight adjustments and efforts worthy of the benefits it promises to deliver.
