GAS Intelligent Humidity Controller

Control the Humidity & VPD in Your Grow Room for Optimum Plant Growth

GAS Intelligent Humidity Controller takes care of the humidity levels in your grow room, for faster growth rates and happier plants. Air temperature and humidity are the two factors that affect something called Vapour Pressure Deficit (VPD). Which is literally the “drying” ability of the air. For plants to grow at their max. The humidity needs to be within the right range for the particular temperature of the air (and the growth stage of the plants). Until now there has hasn’t been an easy solution to optimise the VPD of a grow-space. The Intelligent Humidity Controller changes all that by directly controlling a G.A.S SonicAir Humidifier Pro to achieve the optimum humidity level for the current temperature.

G.A.S. make a version of this Humidity/VPD Controller which can be used with any mains powered Humidifier

  • G.A.S – The leading and most innovative air control equipment manufacturer
  • Directly controls a G.A.S SonicAir Pro Humidifier for the ideal grow-room VPD
  • Doesn’t need plugging into a wall socket; powered from the SonicAir Pro instead
  • 4 modes of operation gives the choice to control humidity or VPD, and to set either constant or separate day/night levels
  • 3 in 1 probe senses temperature, humidity and light (so it knows whether it is day or night)
  • Single control menu system makes setting up easy
  • 3 settings for VPD – Early Veg, Late Veg/Early Flowering, and Late Flowering
  • Set the growth stage and the controller works out the ideal VPD and controls the humidifier for you


G.A.S Humidity Controller for SonicAir Pro Humidifier – x 1
Ready-wired 3-in-1 Sensor on a 3 metre lead – x 1
metre Cable to connect into a G.A.S SonicAir Pro Humidifier – 1 x 5

How the GAS Intelligent Humidity Controller Works:

The Intelligent humidity / VPD controller uses a 3-in-1 probe to sense the temperature, the humidity and the light level in a grow-space. The unit then controls a G.A.S SonicAir Pro Humidifier to either increase the humidity to a user programmed level, or automatically reduce the VPD to the ideal level for the user-set growth stage and day/night phase. For this model of the G.A.S Intelligent Humidity Controller the humidifier supplies power to the controller via the connection cable. No separate mains connection is required for the controller.

There are 4 basic modes of operation which are as follows:

1) Relative Humidity 24 Hours – In this mode the controller will control the humidifier pro in order to increase the humidity to the level set by the user.

2) Relative Humidity Day / Relative Humidity Night – In this mode the controller allows the user to set separate humidity levels for day and night

3) VPD 24 Hours – In this mode the user sets the stage of growth that the plants are in (Early Veg, Early Flower, or Late Flower). The controller then automatically calculates the humidity level to achieve the ideal VPD for the current temperature and the stage of growth and then controls the humidifier to get the humidity into the ideal range.

4) VPD Day / Relative Humidity at Night – During the lights-on period, the unit operates as described in mode 3. However, during the dark-period, it will switch to just controlling the humidity (not the VPD) to a user-set level. The stomata on plants are closed when the lights are off (to prevent unneccessary water loss) because they are not photosynthesising and therefore do not need to transpire. This means that when the lights are off, the VPD is not important. However, high humidity conditions during the lights-off period can encourage mould. It is only important to control the relative humidity during the night, not the VPD.

In our opinion, mode 4 is the best. It controls the VPD during the day when it is important, and controls just the relative humidity during the night when that is most important.

Please Note: While the G.A.S Humidity Controller is a very clever & useful piece of equipment, it can only increase humidity to the correct levels but it cannot reduce humidity levels to bring them within range. However the use of a separate adjustable dehumidifier alongside this controller and a humidifier pro can bring down humidity levels when they are too high.

How to use the GAS Intelligent Humidity Controller

Place the 3-in-1 sensor probe in the middle of the grow space at about canopy height. A circulation fan in the grow-space will increase the consistency of the temperature and the humidity throughout the grow space and is highly recommended.

Next, plug the Controller into your G.A.S SonicAir Humidifier Pro using the blue and black connector supplied on the black 5 metre lead. This cable allows the controller to control the humidifier directly and also supplies power to the controller from the humidifier. Switch on the Dehumidifier. The orange power LED will light briefly and the LCD Display will become active. After the initial lighting of the orange Power indication LED will only come on when the humidifier is being powered.

The LCD display will show the current %RH, the temperature. Whether it is night or day, and whether it is presently controlling RH or VPD.

The menu system is controlled via the knob on the front. To enter the menu system press the knob in. Turn the knob to move up or down through options. Successive presses of the knob will move you through the different sub-menus. If the knob is not turned or pressed for a few seconds. The settings will be saved and the display will go back to displaying the environmental conditions again.

The first menu item is the control type (mode) which is described above. Choose the mode that you want by turning the knob. We would recommend the 4th option: VPDDay/RH NIGHT.

Depending on the mode that you have selected, another press of the knob within a couple of seconds will then allow you to select humidity levels and/or which stage of growth you plants are in (for VPD modes). For modes which involve VPD (such as mode 4) the overridable preprogrammed settings are as follows:

Early Veg Setting maintains 0.4 – 0.8 kPa
Early Flowering Setting maintains 0.8 – 1.2 kPa
Late Flowering Setting maintains 1.2 – 1.6 kPa

Another press of the knob will allow you to override these preprogrammed settings and select your own target VPD.

The next press of the knob will allow you to enter a plant offset. This is the temperature difference between the ambient air temperature and the temperature of an actual leaf. The leaf temperature is best measured with an infra-red thermometer such as our Pocket IR Thermometer. The difference in temperature of the ambient air and a leaf is usually between 1ºC and 3ºC and the usual offset is around about 2.

The controller and probe are factory calibrated. However, if you would like it to match the readings from other equipment that you have then you can adjust the calibration via the “Probe Calibrate” option in the menu. The menu also contains options for choosing the temperature scale (ºC or ºF).

The controller will remember your settings even if the power is disconnected. However, if wish to return it to the factory settings simply unplug the controller from the mains, press and hold the control knob and reconnect the power. Keep holding in the control knob until the display says “Factory Reset Complete”.