The Ultimate Indoor Grow Room Climate Control Showdown

It’s a modern-day gold rush and the wild west for indoor commercial Cannabis growers right now.

The lucky few who have received cultivation licenses plan to cash in bags of green gold IF they do this one thing right …

Missouri is as humid as the Rainforest in the summer and as cold as the Arctic in winter; growing indoors is the only way to achieve a year-round harvest.

With limited indoor space available, maximizing your crop yield is the key to making a fortune.

One of the best ways to do that is by choosing the right HVAC/air quality system for your indoor space. The right decision can increase your post-harvest crop yield by up to 30%! That’s some serious coin er green.

Before we start the showdown, we must mention – Midwest Machinery sells the equipment for all these options. We have no bias towards a particular solution. This showdown evaluates the scientific and business-related facts for the grower. 

Without further ado, let’s cut through the noise and let the showdown begin. Giddyup!

Challenger 1: Traditional “Rooftop” HVAC Units with Portable Dehumidifiers in the Grow Space

The entry-level option. Rooftop air conditioners are installed and sized to handle the room’s cooling load (s) and remove a small portion of the necessary room moisture during the lights-on growing phase. The portable dehumidifiers will try to make up for the rooftop units’ dehumidification shortcomings.

The dehumidifiers have a large job to fill that often gets missed as humidity levels are critical. During the lights-off phase of the room, portable dehumidifier(s) are the primary equipment used to remove moisture.

Here’s the problem, when the portable dehumidifiers are in operation, the air temperature leaving those units is 25°F warmer than the air getting sucked in, this causes the rooftop air conditioners to turn on and try to remove that excess room heat and then quickly turn off again when their task is complete. They are two competing forces.

The frequent on/off operation of the air conditioner causes the expensive compressors within those units to fail much sooner. From the grower’s perspective, this system causes massive temperature, and humidity swings within your grow room space. Your plants will be susceptible to browning, mold, and a much smaller post-harvest yield than in a finely controlled environment. It’s a massive headache for someone trying to grow profitable medical-grade Cannabis.

More information on Rooftop units can be found here


  • Cheapest option.
  • Easy to install.
  • Simple service.


  • No precise temperature/humidity control (units are always fighting each other).
  • Very high utility bills.
  • Comfort cooling solution for people, not plants.
  • Odor control and biological-contamination challenges.
  • No Trending or ability to link everything together for a precise understanding of the space conditions.
  • Often expensive reheat option is still needed to not over cool the rooms.
  • Changing the Rooftop unit’s temperature will mean the dehumidifiers won’t operate the same, and you’ll have to adjust each one independently.

Challenger 2: VRF Units with Portable Dehumidifiers in the Grow Space

VRF systems are very similar to the traditional rooftop unit (challenger 1), with even more challenges for this particular environment.

VRF is a comfort cooling engineered solution. Engineers design and size them for offices, hotels, etc., to handle the cooling load only. Like rooftops, they will remove a small portion of the necessary room moisture during the lights-on grow mode.

There will be many VRF cassettes (The ceiling boxes with vents and fans) in the space delivering cold air to help offset the temperature load of the lights.

Again, dehumidifiers help with the work of the air conditioner in the lights-on mode. The portable dehumidifiers have a tremendous job that often gets missed as humidity levels are critical.

In lights-off mode, portable dehumidifier(s) remove the moisture. The problem is the same as challenger 1 when the portable dehumidifiers are in operation, the air temperature leaving those units are 25°F warmer than the air entering – causing the VRF air conditioners to turn on and try to remove that excess heat and then quickly turn off again when their task has is done.

Frequent on/off operation of a VRF outdoor unit causes the expensive compressors within those units to break much sooner. The grower ends up with the same problems, this system causes massive temperature, and humidity swings within your grow room space. Your plants will be susceptible to browning, mold, and a much smaller Cannabis post-harvest yield than a finely controlled space. Mold is a massive headache for someone trying to grow profitable medical-grade Cannabis.

More information on VRF can be found here


  • Marginally lower utility bills than rooftop units.
  • “Off the shelf” equipment.


  • No precise temperature/humidity control (units continually fighting each other).
  • Very high utility bills compared to our premium options.
  • Comfort cooling solution for people, not plants.
  • There could be odor control and biological-contamination challenges.
  • Many units delivering cold air onto the plants will cause condensation to form on the leaf, leading to mold.
  • VERY HIGH levels of refrigerant pumping around the space are incredibly unhealthy if there is a leak.
  • Lots of compressors and fans between the VRF systems and the portable dehumidifiers. Even more failure points and expensive repairs to consider.
  • There is no Trending data or ability to link everything together for a precise understanding of space conditions.
  • Changing the VRF system’s temperature will mean the dehumidifiers won’t operate the same, and you’ll have to adjust each one.

Challenger 3: Chilled Water System

Download our chilled water vs. DesertAire infographic

We’re getting into better options for Cannabis grow rooms. However, we still believe a chilled water system is not the best option most of the time.

Imagine buying all the parts to a car and assembling a unique vehicle for the first time. This is the analogy for using a chilled water system on grow rooms.

Every building must be designed/configured by highly skilled engineers with extensive experience with indoor grow rooms. For room controls, they must be custom coded by experienced programmers. There are very few programmers at standard controls companies familiar with the control of indoor grow spaces.

A heat exchanger array controls the room temperature and humidity. Chillers make cold water and send it to air handling units (big metal boxes with fans and coils). Air handling units blow air across the cold-water coils to send cold air into the grow space. To keep from overcooling a Cannabis room, a massive amount of “reheat” is necessary. This is often in the form of electric reheat coils (this is a giant energy hog). The chiller also needs help from large cooling towers that sit outside of the building.

There will also be extensive water piping throughout the building with pumps that send the water through the pipes. System pieces will be tied together by a controls contractor, who doesn’t work for the same company as any equipment.

Sometimes when there is a problem, every equipment provider and trade point their fingers at each other, and the customer gets stuck in the middle with no answers.

For Cannabis grow rooms, we cannot recommend a chilled water system in most cases.

More information on chillers can be found here


  • High energy efficiency.
  • Expandability (if planned).
  • Potential for very robust equipment.
  • Higher crop yield can be achieved.


  • Complex system design.
  • Potential redundancy issues if the chiller breaks.
  • Repairs for large equipment is expensive.
  • You’ll call a specialized service company for maintenance and service.
  • 3rd Party controls contractor not associated with the equipment (finger-pointing if something isn’t working).
  • Owners can’t change settings easily without involving the controls contractor to write new software.
  • There is a high cost of electricity due to reheating necessity.
  • Costly as is large commercial/industrial equipment.

Challenger 4: Specialized Grow Room Dehumidification Systems with Total Energy Recovery Wheels

We’re getting closer to what we believe is the best system for an indoor grow space, and this system is meant for indoor Cannabis facilities. However, this type of equipment only sees useful applications in particular environments.

To break down this unit style, picture the rooftop unit from Challenger 1, and add a total energy recovery wheel. A total energy recovery wheel allows you to move heat and humidity from the wheel’s indoor side to the wheel’s outdoor side and vice versa. Wheels are a phenomenal energy savings source for comfort cooling/heating in an office or school. But as we’ve seen from the other challengers, what’s right for people, typically isn’t suitable for plants unless you like wasting energy and paying high electric bills.

Units of this style are relying heavily on the Outdoor Air (OA) temperatures and humidity to help dehumidify and heat/cool the space. In some US locations, these units are viable, but this poses a HUGE problem for indoor growing in most areas. 

  1. The whole point of moving a grow room indoors is for consistent temperature/humidity AND to remove the possibility for airborne pollen, mold spores, and pathogens in the air that can RUIN YOUR CROP. 
    1. Because of mold and pollen, they utilize extremely high-quality HEPA filters. These are VERY EXPENSIVE and require A LOT of MAINTENANCE. They also aren’t 100% effective; there’s still a margin of error to ruin your crop. 
    2. Most grow spaces required some outdoor air per code, but do you want to gamble with introducing more OA than you have to? Minimizing the amount of OA you have to filter reduces the risk of ruining your crop. 
  2. If either the temperature outside, or the humidity outside, is higher than the temperature and humidity you need for your plants, THE WHEEL WON’T WORK.
    1. This is something to think hard about when considering this type of unit. Remember, dehumidifying is our biggest challenge in providing the proper conditions for high yield and high-quality plants.
  3. In cool and dry locations, like Colorado or Northern California, the wheel will utilize OA and save energy.
  4. In climates like St. Louis, between 40 and 70% of the time, your wheel will be completely ineffective. That’s more than half the year!
    1. When the wheel is ineffective because it’s too hot or humid outside, these systems have all of the same negatives as the challengers above – extremely expensive electric reheat and likely even a need for additional inefficient standalone dehumidifiers. 
  5. These systems implement a total energy wheel. There are essentially three types of wheels for energy transfer: Sensible (temperature only), Latent (humidity only), Total Energy (temp and humidity). 
    1. A total energy wheel sounds like the best of both worlds, right?! Well, you are sacrificing a little of the ability to transfer both the temperature and humidity each so that you can do both with one device. 
    2. Remember, we heavily focus on dehumidification, and we just found out that dehumidification is inhibited because of the wheel type. You’re going to need more expensive cooling and reheat to make up for that deficit. 


  • If utilized in dry and cool climates, these units have the potential to produce some energy savings.
  • Purpose Built Machine
  • Factory Controls for indoor grow spaces.


  • Increased chance for outside contaminants to come in and ruin your crop.
  • Requires your grow facility to be located in a moderate climate to work correctly.
  • When the wheel isn’t able to help, you now have very high utility bills.
  • No local service and support.
  • Wheel Maintenance is costly.
  • HEPA Filters are expensive.
  • Traditional Technicians will need specialized training on wheel maintenance.
  • Third-party manufacturing and construction of units.

Challenger 5: DesertAire™ GrowAire™ Environmental Control System

A DesertAire™ GrowAire™ purpose-built (all-in-one) environmental control system is a fully integrated solution that performs the air conditioner’s work and the dehumidifier by using highly advanced; Cannabis industry designed control logic to handle the temperature and humidity … All in one package!

Since this option is all-in-one, the system controls can easily remove heat or add it back into the indoor space as required during light-on and lights-off cycles.

These units use a compressor to help cool the air to handle the temperature load. Part of the refrigeration cycle that allows them to cool the air also gives these units the ability to reheat when necessary. This means we don’t need any extra reheating equipment. We call this “free reheat” because the energy was already created when removing the heat to cool the air.

All of this is built into the computer controller, and because the controller is handling it all, you can easily change setpoints without fear of causing the system to fight itself.

GrowAire can be a set-it-and-forget-it system where the computer does all the work for you and manages the equipment, or the grower has complete fine-tuned control to their desires.

Grow rooms using this system typically see very healthy and robust plants. We have seen a 30% increase in post-harvest crop yield vs. other system options in some installations.

Visit our in-depth article on Desert Aire purpose-built Cannabis systems here


  • Purpose-built system.
  • Purpose-built controls system.
  • The exact temperature and humidity control required.
  • Controls system built by the manufacturer of the equipment (no finger-pointing).
  • Free reheat – no need to pay for a unit to cool and another unit to heat (dehumidify).
  • Electrical company rebates are easily acquired.
  • A multitude of contractors can maintain equipment.
  • Remote support from the factory available at a moment’s notice (AireGuard).
  • Reduced total number of pieces of equipment (less to maintain and fail).
  • Higher crop yield and profit potential.
  • Thousands of Installed Unit.
  • Years of proven reliability and operation.
  • Local service and support.


  • Higher up-front cost (offset by energy rebate).
  • Planning is required to avoid equipment production lead times.

There you have it, folks! A purpose-built system like DesertAire™ GrowAire™ is the best option based on science, long-term cost analysis, and maximum post-harvest margin. If you’re longing for more information, don’t hesitate to download our ultimate grow room design guide below or reach out directly to start planning your room design. Talk soon.

air quality guide