Guide to Grow Room Air Circulation Using Fans

A good growing environment should provide the optimum conditions for growing your plants. We can emulate those ‘perfect’ conditions 24/7 by keeping everything in our sealed and controlled grow room at these optimum levels. This is also why we favour using grow tents – because the conditions within the grow tent are that much easier to control. Air circulation and ventilation is part of that mix of perfect conditions we can treat our plants to. So here’s how we can make the best use of fans for that purpose.

Plants growing outdoors benefit from gentle breezes, perpetually circulating air, and occasional strong winds. We need to emulate these things within our growing area as much as possible (while leaving out the strong winds). We control things like temperature and humidity inside the grow tent, and we emulate natural sunlight with grow lamps, so in the same way, we should provide controlled air circulation as well.

Why Do You Need Air Circulation in a Grow Room?

We’ve already looked at ventilation in another article, so here we’ll consider only air circulation and how a healthy circulation of air is good for our plants and a healthy and bountiful crop at harvest.

There are many good reasons we should provide good air circulation and ventilation in the grow room. Plants developed over millions of years to adapt well to outdoor breezes; they thrive in good air circulation. Let’s consider each of these in turn.

Controlling Humidity in the Grow Room

Humidity is an important aspect of any well-controlled grow room or grow tent. It needs to be more or less continually monitored.

If the humidity is too low, plants will stop growing as they dry out, being starved of water and the nourishment of the nutrient solution. On the other hand, if the humidity is too high, you’ll only be encouraging pests and diseases. Venting humid air through ducts to the outside is handled by the ventilation system. The fans ensure that the correctly humidified air within the growing area is uniformly distributed.

We want to keep humidity between 50 and 60% in the growing area. If all the plants are growing at the same rate and at the same stage in development, we can further control the humidity in the vegetative stage of the plants, which is the point where the plants start growing a lot of leaves that are thirsty for moisture. During this early stage in their growth cycle, they need about 70% humidity, which can easily be provided.

Controlling Transpiration in the Grow Room

Transpiration is a process where water moves through the plant and how it evaporates from the leaves, flowers, and stems. Good air circulation emulates the breeze of the outdoors, allowing better absorption of water and, in this case, of the nutrient solution and all the nourishment within it.

Removing Excessive Heat in the Grow Room

Heat is inevitable from the grow lights used in the grow tent or growing room. The optimum temperature here is somewhere between 23 and 27 Celsius. Early on, the plants’ vegetative stage will prefer it about one degree Celsius warmer for both the maximum and minimum limits.

Some grow lights come with their own cooling systems, and whatever the circumstances, grow lights will need their own cooling and ventilation in the vast majority of cases; some lights give off more heat than others.

Cooling and ventilation systems will play their part, but good air circulation is also essential. It is also useful in terms of:

Preventing Hot Spots in the Growing Room

In any growing room or grow tent, there will be places where heat accumulates if unchecked. These places tend to be corners and out-of-the-way places, the ‘nooks and crannies to be found where it’s difficult to reach. Good air circulation will ensure that heat does not accumulate excessively in any area and attempt to regulate conditions to uniform the ambient temperature throughout the growing space.

Avoidance of Microclimates in the Grow Room

Similar to the hot spots mentioned above, you want to avoid what are known as microclimates from developing and establishing themselves within your growing area. This is where oddly imbalanced areas of humidity, temperature and carbon dioxide levels may develop.

The use of fans will prevent this, reducing the incidence of mould and disease developing, ensuring humidity, temperature, and CO2 uniformity. You really don’t want to continually have to deal with one or two known problem spots if you can help it; adequate air circulation will prevent this from happening in the first place.

Managing Wind Stress in the Grow Room

Plants constantly subjected to breezy, buffeting wind outdoors will strengthen such plants, especially their stems. So it’s always good to emulate this wind artificially in the grow room or tent. Good air circulation goes part of the way towards emulating the effect of wind. In this way, you’ll be sure of a more robust crop than it would otherwise be.

Preventing Disease and Bacteria in the Grow Room

Bacteria, diseases and the pests which spread them can be prevented to a large extent by good air circulation. Fungus gnats and spider mites love humid conditions where the air is motionless and stagnant. Fans can play their part in blowing the pests’ eggs off their favourite growing spots and drying out the damp areas favoured by these bugs and their larvae.

Mildew and mould also prefer stagnant and humid conditions. Good air circulation helps establish an unwelcome environment for these pests so that they find it harder to live and breed, preventing the conditions that bring about disease.

Controlling Carbon Dioxide Flow in the Grow Room

Plants drink in carbon dioxide (CO2) and give out oxygen (O2). In the sealed conditions of the grow tent, this carbon dioxide will reduce gradually as the plants consume it, while O2 levels will increase. While it is the ventilation system, and not the fans, which replenish the air with fresh CO2 from outside, the fans you use will ensure good circulation and ensure that the CO2 is evenly distributed throughout all the plants, wherever they are in the grow room.

Proper Air Circulation Protects Your Investment

A final consideration is cost. Having invested in a grow room and all the equipment and kit necessary for a good growing environment, you’ll want to ensure that your investment is protected. In general, good air circulation is healthy for everything inside the grow room, and your equipment and resources will all last longer if treated well.

How do You provide Good Air Circulation in Your Grow Room?

Circulation and ventilation are often discussed together. We’ve already had a look at ventilation in some detail, together with worked examples of how to calculate the power rating of the extractor fan or fan-filter system you need for your growing space. Here we’ll only look at the air circulation, how to best achieve it and what it means for the health of your plants.

Oscillating fans in the Grow Room

Ideally, you will want to use fans that emulate the randomness of outside air breezes and wind. Oscillating fans can best achieve this. These should be strategically placed in your grow room or tent for the best effect.

Oscillating fans are relatively cheap and serve a very good purpose. They will provide the proxy breezes, which will cause air to circulate under, above, below and around your plants, and they will do this continuously. This evens out air circulation and the distribution and quality of the air and strengthens the plant stems. It also further removes the possibility of hot spots developing.

When you first start using these oscillating fans, you’ll be able to move them around to find the best place for them, as they’re pretty small and easily portable. The task is to find the best place for them and then keep them there and switched on all the time, or at least most of the time. You will need several such fans for your growing area. Don’t point fans directly at the leaves; the resulting so-called windburn may result if the ‘breeze’ is too strong or relentless.

How to Use Oscillating Fans in the Grow Room

Here’s how you could put your oscillating fans to best use in your grow room or tent. You may experiment with these, chopping and changing to see which works well for you and your plants.

Move Your Fans About

You might want to try just moving your fans around different parts of your growing area to start. While never allowing your fans to point at the leaves of plants directly, you should also experiment with different directions to point the fans in so that they circulate air freely under, over and between your plants as evenly as possible. Find the optimum positions and directions for each of your fans within the growing area.

Make Use of Clip-On Fans and Attachments

In support of the above, you may want to invest in a couple of clip-on fans placed in areas otherwise difficult to get at. As you experiment with the above scenarios, you may find that problem spots will likely emerge as places to turn your attention to, and these will probably be in parts of the room where access isn’t easy.

You can get small fans (available in sizes from four inches and upwards) that clip onto a handy surface, and they’ll be able to deal with awkward areas. As well as helping air circulation, using your fans strategically like this can cool places that become hot otherwise, such as in areas where there are concentrations of grow lights.

Mix Your Circulating Air Using a Diffuser

The use of an air diffuser makes sure that the air circulates in as wide a dispersal as possible. It works by venting the air coming from the fan through ducts. Many diffusers are circular and ensure that the air travels at 360 degrees in all directions.

You want to make sure that your diffuser fan spreads the air evenly around, avoiding the risks of windburn or similar issues. There are several manufacturers of these, and they each provide sound advice on how best to make use of their products.
You’ll likely have the whole grow area covered nicely with multiple fans and diffusers!

Working Your Fan with a Humidifier

You may be using a humidifier, in which case you’ll want to ensure an even distribution of humidity throughout the growing area.

Humidifiers work by sending out a fine mist of water into the air. This augments the existing humidity so that you can fine-tune it. Humidifiers are sometimes used when the prevailing conditions are arid to the extent that the air needs additional water droplets to increase humidity.

If using a humidifier, be aware that you should only use distilled water, not tap water. The minerals in tap water can interfere with the grow room’s controlled environment, particularly in hard water areas. Over time, the minerals from tap water may solidify into very fine, crusty lime deposits.
To use your fan with a humidifier, position your fan to blow air directly into the path of the mist coming from the humidifier to ensure an even and constant humidifying result.

Air circulating fans are a necessity for your growing area. I hope this article has shown the solid reasons for investing in one or several, depending on the size of your hydroponic system. As you experiment with these, your experience and confidence will grow, and you’ll be one step nearer to creating the optimum conditions necessary for producing a fantastic harvest!