Clean Air Act: the lowdown on air circulation

By Hydrofarm’s Kelley Ryan

When setting up an indoor garden, air circulation and exhaust are just as important to your overall plant’s health as water and light. A successful gardener can use airflow to control temperature and humidity, which will help prevent disease and eliminate hot spots.

So…what’s the best way to set up your exhaust?

Keep in mind that hot air rises, so the best place to set up your outgoing air is at the top of your room, and intake should be closer to the floor where the air is cooler. It’s important to note that an intake fan is not always necessary; a passive intake can work well in some gardens (passive intake occurs without a fan—the exhaust fan creates negative pressure in the room and naturally draws in fresh air).

Oscillating fans circulate the air inside of your room, minimizing hot spots. They don’t create enough airflow on their own to cool your space, but they’re essential to a successful garden. Fresh air and movement can help stimulate stem growth and can prevent mold, especially on flowers.

 Let’s start simply.

Optimal temperature ranges from 65°F to 80°F, and it’s best to keep your humidity level close to 50% when flowers are present; humidity can be higher in the vegetative stage. With this in mind, you’ll want to have at least one fan for exhaust and another for circulation. To effectively exhaust your grow room, the air needs to be completely exchanged every 3-5 minutes. There’s a simple equation you can use to help you choose the fan with the right CFM rating.

 CFM = Cubic Foot per Minute

Length x width x height/3 (or 5) = CFM needed to completely exchange the air. Keep in mind that this is only a calculation for air exchange and doesn’t take heat levels into consideration. As a general rule of thumb, double the CFM calculation for effective heat exchange and invest in a fan speed controller to keep the fan running at the speed required to keep the room just cool enough.

In addition to fans, many growers will invest in a carbon filter.The carbon filters on the market today ensure that the air exhausted from your grow room has been scrubbed and is free of any odor. Be aware that a carbon filter is only as good as the quality of carbon it contains. Filters are also sold with a CFM rating, and you’ll want to match the CFM on the filter with that of the fan you’ll be using with it.

Taking the time to make sure your room has the correct amount of airflow and exhaust will eliminate future headaches, I promise! You’ll sleep better knowing your plants are thriving in an ideal environment free of stagnant air, hot spots and molds.