Rooftop air conditioners can be installed and sized to handle the cooling load of the room(s) and will 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 very 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 has been completed. They are two competing forces.


The frequent on/off of an air conditioner causes the expensive compressors within those units to die 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 a finely controlled space. This is a huge headache for someone trying to grow profitable medical-grade Cannabis.


Pros and cons of traditional "rooftop" HVAC units with portable dehumidifiers in a grow facility


  • Cheapest option
  • Easy to install
  • Simple service


  • No precise temperature/humidity control (units are constantly 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 temperature on the rooftop unit will mean the dehumidifiers won’t operate the same and you’ll have to adjust each one independently.

For more information read the blog, “The Ultimate Indoor Grow Room Climate Control Showdown

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