How to Perfect Your Grow Room Dehumidifier Setup

This article is sponsored by Quest Dehumidifiers.


When the team at East Coast Cultivation set out to build its new indoor grow operation in Rhode Island, it knew it had to nail one thing: environmental controls.

“The key factor in having a successful grow is controlling your environment,” said East Coast Cultivation CEO and co-founder Joe Welch. “Once you lose control of your environment, the serious crop-crushing issues begin to take hold.”

East Coast Cultivation cannabis growing facility in Warwick, Rhode Island. (Quest Dehumidifiers)

The two main “crop-crushers” are concerns many growers face at one time or another: powdery mildew and botrytis, more commonly known as bud rot. Either of these issues can destroy a grow and lead to thousands in lost revenue.

With that knowledge, Joe Welch and his team, including COO and co-owner, Susan Welch, put a significant amount of time into dialing in their grow room dehumidifier setup. That setup, along with an HVAC system, is the backbone of a well-controlled environment, said Welch.

To fine-tune a setup, growers need to focus on three things when it comes to their dehumidifiers said Coleman Retzlaff, a factory representative at Quest Dehumidifiers, which provides commercial units to hundreds of cannabis cultivators nationwide: proper sizing, placement, and air flow.

Strength in Numbers

“Water in equals water out,” is the mantra for growers trying to dial in their humidity levels. It may sound simple, but it’s a little more complicated in practice.

Plants release nearly all of the water they absorb back into the air, so in a sealed grow room, cultivators need to account for and remove that water from the air to ensure proper humidity levels. If a grower uses 25 gallons of water daily, for instance, and 5 gallons go down the drain, that grower is left with 20 gallons. There are eight pints per gallon (dehumidifiers are measured in pints per day), so you need to be able to remove about 160 pints per day from the air.

“When we do this calculation, it really is that simple,” said Retzlaff.

One common misconception that leads to under-sizing a grow room dehumidifier setup is the idea that having an air conditioner means additional humidity control isn’t necessary. While air conditioners can remove some moisture, they are designed to cool, not remove water, and therefore don’t keep pace with the needs of a grow environment.

Maintaining a dehumidifier in the grow room at East Coast Cultivation. (Quest Dehumidifiers)

What’s more, air conditioners rarely run at night when the lights are off and there’s no additional heat added to the room. These are exactly the conditions that can allow mold and mildew to take hold. At East Coast Cultivation, Welch and his colleagues found it was better to oversize their dehumidifier setup with equipment that let them prepare for potential worst-case scenarios.

“The single best tip for dialing in your humidity is to size your units properly and have dehumidifiers that work with automated controls,” said Welch.

He’s in good company on that advice. Seth Lee, operations manager at Denver’s Greenlight Cannabis Company, did the math for how much water his flower room will use when plants are releasing the most water. He runs six dehumidifiers, each capable of pulling 225 pints of water from the air daily. Lee admits his flower room may feel slightly over-engineered—but he’d rather be safe than sorry.

“If you don’t invest in proper environmental controls, it’s almost negligent,” said Lee. “You’re setting yourself up for failure because controlling humidity is a key part of an integrated pest management strategy, and I include mildew and fungus as pests.”

Perfecting Placement

Whether a grower is running a single dehumidifier or a ten-strong legion, proper placement is key to their effectiveness. Knowing how to place dehumidifiers helps to maintain a stable environment and reduces the risk of creating microclimates where humidity spikes and mold can take hold.

To ensure proper placement, Lee advises growers to leave even spacing between each dehumidifier. It’s also vital that growers pay attention to details, like facing the filter side toward the middle of the room and checking regularly to confirm each unit is draining properly.

“We run dehumidifiers above the lights to save space and rely on good airflow from fans to keep the air evenly mixed,” Lee said.

Seth Lee monitors the grow room at Denver’s Greenlight Cannabis Company. (Quest Dehumidifiers)

As grow rooms increase in size, Retzlaff said spacing has become increasingly important because it allows for zoned humidity control. For example, rather than running 15 dehumidifiers at once and then turning them all off, each is automated to sense independently when humidity increases in its zone. This approach keeps the room’s relative humidity more stable and increases energy efficiency, he said.

At East Coast Cultivation, head growers and co-founders Alex Welch and Tyler Greenless opted to go with a modular approach instead, spacing the dehumidifiers so that if one needs service, the others can maintain proper humidity levels in its absence. “You need to build in redundancy,” Greenless said. “We’d rather have three units pulling 225 pints each than one pulling 700 pints. If that 700-pint unit fails, you have no backup, and if it’s not serviced quickly you risk a humidity spike and mold growth.”

Attention to Air Flow

Finally, understanding the shape of each room and how air will flow and mix in that space is critical to ensuring any dehumidifier setup maintains a consistent humidity level in a grow room.

In a long room, growers need dehumidifiers spaced equally to create a circular air flow. If the room is narrow, with one dehumidifier, Retzlaff said discharged air can be pushed over the room to get a consistent air mix across the plant canopy. That’s a stark contrast to a tall room, where growers may want to duct return air down to the floor to create a consistent air flow.

“We can duct our dehumidifiers from the supply and return ports to direct air where growers want it and in the way that works best for their environment,” Retzlaff said. “That added bonus can play a big role in establishing consistent humidity levels.”

For more resources on environmental controls, mildew prevention and humidity tips, check out Quest’s Grow Info page.