Garden & Greenhouse


Ventilation System Automation for Small Greenhouses and Indoor Gardens

The ventilation system of a small greenhouse or indoor garden is one of the most crucial systems found in “controlled” horticulture. After all, it is the ventilation system that keeps the temperature, humidity, and CO2 levels in check. The term “ventilation system” refers to a network of equipment, which may include fans, air conditioners, heaters, evaporative coolers, dehumidifiers, humidifiers, air purifiers, filters, and/or CO2 enrichment equipment.

Some greenhouses or indoor gardens will utilize many pieces of equipment, while others may require only a few. The amount of heat to be removed, along with the size and location of the garden, will determine the type of equipment a gardener will need to provide his or her plants with adequate atmospheric conditions. Plants love consistency and the atmospheric conditions are no exception. Ultimately, the components of a garden’s ventilation system and how they are automated will be the determining factors over the consistency of the atmospheric conditions.

Heating and Cooling

The most basic, yet important, purpose of any ventilation system is temperature control. Although rarely used by indoor horticulturists, electric or gas heaters play an important role in maintaining proper temperatures in a greenhouse. This is especially true for greenhouse horticulturists who like to operate their greenhouses during the cooler late fall or winter months. For most small greenhouses, a portable electric heater or a gas heater is usually sufficient. Most electric heaters include a built-in heating thermostat which allows the user to set the desired temperature. When the temperature drops below the set-point, the built-in thermostat triggers the heater to come on. Once the desired temperature is achieved, the thermostat automatically turns off the heater. Heaters without built-in thermostats need to be plugged in to a heating thermostat or an atmospheric controller for automation.

A cooling thermostat will trigger a device in conditions that are the exact opposite. Instead of triggering the device when the temperature gets too cold, a cooling thermostat triggers a device when the temperature is too warm. An independent cooling thermostat is a common automation device used in indoor gardens or small greenhouses to control the exhaust and/or intake fans. Greenhouse gardeners can use a wide variety of cooling techniques, including passive vents for convection heat transfer and/or evaporative coolers. Mechanical fans are commonly used in both indoor gardens and hobby greenhouses. In most cases (except for the convection heat transfer), a cooling thermostat or an atmospheric controller can be used to automatically control the device(s) and maintain a consistent temperature.

Cooling with Air Conditioning

Although most greenhouse hobbyists rely on other cooling methods, it is not uncommon for indoor gardeners to use air conditioners as the main cooling device. One of the most popular types of air conditioners used by modern indoor horticulturists is the mini-split air conditioning system. These types of air conditioners are very efficient at removing excess heat and maintaining optimal temperatures. When shopping for an air conditioner for an indoor garden, a gardener needs to pay close attention to the air conditioner’s BTU rating. British thermal unit, or BTU, is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Don’t let the definition of BTU confuse you. Instead, just think of BTUs as a way to quantify heating or cooling equipment. In other words, a grower can use a BTU rating to find the appropriate size air conditioner for his or her garden. However, for indoor gardens it is not just the size of the room that will determine the required BTU rating. To adequately cool an indoor garden, a horticulturist will need to consider five major factors that influence the required BTU rating of an air conditioner. Those factors are: the dimensions of the growing area, the lighting equipment, the ballasts of the lighting equipment, the CO2 equipment, and any other device or equipment that will affect the room’s heat load.

Automating Air Conditioners

The great thing about the vast majority of mini-split air conditioners is that they come complete with built-in temperature and humidity control. Put another way, they have a thermostat and humidistat built right into the device. This means a grower can set his or her desired temperature on the air conditioning unit itself. Air conditioners without built-in thermostats can be automated with the use of an atmospheric controller.

Atmospheric Controllers

Atmospheric controllers are devices that usually feature both a thermostat and a humidistat. Essentially, the temperature, humidity, and air exchange of the garden space can all be automated with this type of controller. Atmospheric controllers have the capability of controlling multiple devices at once, including humidifiers/dehumidifiers, intake and exhaust fans, and CO2 enrichment equipment. Atmospheric controllers that control multiple devices can also be referred to as multi-controllers or a “brain” system.

The biggest advantage of controlling all ventilation equipment with a single device is heightened efficiency. For instance, it is counterproductive for a grower to operate his or her CO2 enrichment device at the same time their exhaust fan is removing air from the environment. When the CO2 equipment and exhaust fan are plugged into the same atmospheric controller, the device will automatically disable the CO2 equipment when the exhaust fan is operating. This reduces wasted CO2 and heightens the overall efficiency of the ventilation system.

Some of the latest high-tech atmospheric controllers even contain special microprocessors and customized algorithms. These particular controllers can actually “learn and react” to the garden’s conditions. For example, let’s say every day at noon the greenhouse or indoor garden’s temperature suddenly rises beyond the desired parameters. The controller turns on the air conditioner or exhaust fan to correct the problem. Over an extended period of time, if the same issue happens at the same time each day, the controller will recognize the pattern and act intuitively to correct it. In this example, the atmospheric controller would automatically turn on the air conditioner or exhaust fan at 11:45 a.m.; just before the temperature rises above the desired parameter. These “smart” controllers provide the most consistent environmental conditions possible.

Controlling CO2

Not all indoor gardens or hobby greenhouses have CO2 enrichment as part of their ventilation systems. Gardens without CO2 injection systems must rely on fresh air intake as a way to replenish CO2 in the growing environment. Horticulturists who wish to enrich the garden environment with CO2 should incorporate some sort of CO2 control system. Most modern atmospheric controllers come equipped with built-in CO2 control systems. There are also stand-alone CO2 control systems available. A good CO2 controller will essentially automate the CO2 system, controlling both the concentration and the appropriate times for operation. Plants thrive in consistent environmental conditions and the concentration of CO2 needs to be consistent as well. The amount of CO2 in the growing environment is detected by a CO2 “sniffer”. The “sniffer” periodically samples the atmosphere’s concentration of CO2 and then sends a signal to the atmospheric controller or independent CO2 controller. If the concentration falls below the system’s set-point, the controller will then trigger the CO2 device to turn on.

Controlling and Monitoring from Remote Locations

The newest and most exciting additions to ventilation automation are software-based control systems and wireless garden devices. These systems serve the same purpose as traditional automation equipment, but

provide additional control features, such as remote access to the devices and data logging. In fact, many of the new wireless automation devices can be monitored and controlled from a mobile device. This means that much of an indoor garden or greenhouse’s ventilation system can be controlled from anywhere a gardener can get an internet connection. Perhaps the most distinct advantage of a wireless automation system is that it allows the grower to log significant amounts of data that can later be reviewed or compared. Comparing data from previous gardens gives vital information to the gardener and allows him or her to experiment with various techniques. For example, data logging of CO2 levels can provide valuable information over the course of a few garden cycles and help a gardener determine the optimal concentration of CO2 for his or her particular crop. All in all, the ability to log and compare data over a long period of time gives horticulturists the tools they need to continually improve their craft.

Maintaining consistent temperatures, humidity, and CO2 levels within an indoor garden or hobby greenhouse are just as important to the success of the garden as lighting or nutrition. Indoor horticulturists and greenhouse growers who use atmospheric controllers will be able to automatically provide their plants with the proper conditions for accelerated growth. With the recent advancements in automation technology, gardeners are able to monitor and control their garden’s atmospheric conditions from virtually anywhere in the world. Ventilation systems that feature automated alerts can even notify the gardener in emergency situations, thus saving the garden from utter catastrophe. All in all, the more automated a ventilation system is, the less a gardener has to worry about the atmospheric conditions. Ventilation automation not only saves time and money, but also provides priceless peace of mind to indoor horticulturists and greenhouse hobbyists.

Suggested Vendor Profiles

Smart Quibix™

We designed Smart Quibix™  with the serious gardener in mind. Use Smart Quibix™  to keep an eye on your grow parameters and control your equipment based on parameter values or the solution’s scheduling interface. The brains of Smart Quibix™ is a robust plant monitoring solution with many unique and useful features – How’s my plant?™ (HMP). HMP’s tools include a grow log, alerts, and drill-down and granular reporting. When used without an internet connection, access HMP on the LCD screen of the Smart Quibix™ controller unit or through other devices on your local network. Want to access and control your garden with Smart Quibix™ remotely? Use HMP to keep tabs on and maintain your garden from anywhere, anytime using the intuitive HMP Web and Mobile interfaces. In addition to offering protection against catastrophic failures, Smart Cubix™ will also help you repeat your successes. Plant needs and sensitivity regarding temperature, humidity, soil moisture, etc. can vary considerably. Use HMP to customize optimal parameter zones based on the needs of your plants. Every time you grow a new plant or cultivar, use HMP to save your settings as plant profiles. Saved profiles can be used later or shared with other growers. Smart Qubix™ works in indoor gardens, in greenhouses and outdoors. You can even include real-time local meteorological data further expanding suitability for a broad range of horticultural scenarios.  For more information visit

Plug N Grow™ Controllers

Founded in 1995, Nova Biomatique (2011) Inc. develops, manufactures and commercializes indoor and greenhouse climate controllers for professional and amateur gardeners. Our controllers are sold under our trademark Plug N Grow™ Controllers. Based in Eastern Canada, Plug N Grow Controllers is one of the only climate control company that manufactures 100% of their products right here in North America. Since 1995 Plug N Grow Controllers main mission is to offer top of the line North American made climate controllers for every grower. We have been known for our reliable controllers that are backed up with our hassle-free warranty. We stand behind every product that leaves our facility. Our technical support staff is there to help our customers, simply call our toll-free number and a qualified agent will assist you in any matter. Thank you for choosing Plug N Grow™ Controllers and we look forward to helping you increase your yields. Plug N Grow Controllers are available through your local indoor garden retailer. Simply ask for Plug N Grow climate controllers. For more information call 888.577.6274, Email or visit

Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability. He is a Garden & Greenhouse senior editor and can be contacted at

Some of the images for this article were provided by Smart Quibix™ and Plug N Grow™ Controllers

Read More Articles

Promoting Greenhouse Ventilation and Dehumidification

The Basics of Greenhouse Ventilation

The Importance of Ventilation in a Greenhouse

Ventilation System Automation for Indoor Gardens and Greenhouses

Click Here for  a Free Garden & Greenhouse Magazine Subscription

Click Here for a Free Garden & Greenhouse Email Newsletter Subscription