FAQ: CLIMATE CONTROL

The easiest method is to install a vent fan on a timer. The timer will regularly turn the vent fan on and exhaust humid air. While this will help considerably it is still a very rough method of control. We prefer more precise humidity control and therefore use a vent fan powered by an automated controller which will keep the RH level within a set parameter. The controller will sense the RH level in the room and will turn on the vent fan whenever humidity levels reach too high. It will turn the fan off when the RH level has fallen below your chosen set point. Here’s an example of a controller we like, the HUM-1 from C.A.P.

In a medium to large-scale system, you may find that a vent fan is not sufficient and that a dehumidifier must be employed to solve the problem. Most dehumidifiers you’ll find on the market are not strong enough to handle this sort of situation. They also require regular emptying of the collected water which can be a real pain (although you can and should use this water as it is usually very pure!). We suggest using an industrial-strength dehumidifier which pumps directly to a local drain.

To increase the relative humidity around your plants, place them on a bed of gravel in a water-filled saucer. Place th e pot on the gravel, but do not allow the water to touch the pot, to avoid problems with root rot. A humidifier also gives excellent results. A humidifier can be run with a timer – with the help of a hygrometer you can experiment to find how long you need to run it to achieve the optimum level of humidity. Another alternative (and one which we prefer ourselves) is to run the humidifier with the help of an relative humidity controller such as the HUM-1 from C.A.P. A third option is a humidifier which can be connected to a water supply for continuous running.

How do I add CO2 to my garden? What do I have to worry about?
The first thing to decide is which method you want to use to enrich your room. The goal is to fill a room with the desired level of CO2 as quickly as possible.

A CO2 Injection System runs off of carbon dioxide gas (much like a soda dispenser) and is a good choice for a small room. The drawbacks to this kind of enrichment system is the need to consistently change CO2 tanks, and the fact that it can often take a long time to enrich a room. It's a great choice for smaller systems. The largest room this system should be used with is 10x10 (and that’s pushing it a little). We've designed a CO2 Calculator to help you figure out how long to run your emitter system.

We prefer to use a CO2 Generator for larger rooms. Generators come in different sizes and you can purchase a generator that is optimum for your room size. (You want a generator that is capable of enriching your room in 5 – 10 minutes.) We have a Calculator to help you choose the correct size generator.

CO2 generators use one of two types of fuel.  You can choose to run it off of liquid propane tanks or a natural gas line.  Liquid propane is fine, but the tanks need to be regularly refilled (which can be a real pain).  Natural gas runs off of a natural gas line, which once installed properly, is safe, low maintenance and easy to use.

CO2 emitters do not add any extra heat to a grow room, although CO2 generators do. Depending on the size of generator you choose, you may be adding a considerable amount of heat to your grow room. This combined with grow lights can create a very warm room indeed. The good news is that heat is a necessary catalyst for plants to use the added CO2 and that they prefer much warmer temperatures than they do without CO2 enrichment. Most plants prefer temps of up 90 – 95 degrees with CO2 enrichment. If your room doesn’t heat up this warm you may need to bring in a heater (this can be the case for greenhouses).  Usually, however, the room will get too hot and an air conditioner will be employed.

Humidity is the second major issue with CO2 enrichment.  CO2 enriched rooms can get extremely wet. This increase in RH is due to the fact that the plants’ metabolic processes are occurring at a more extreme rate and water is flowing up through the roots and out of the leaves quickly. Most plants do not thrive in an overly humid environment. Most plants prefer an environment between 55 and 65 RH. The preferred level of humidity fluctuates as the plants move through their seasons. They will like more humidity in the vegetative stage and less in the fruiting/flowering stage. As the plants grow older, more leaves are produced and more moisture is created. This will become a problem for most growers (although this will vary depending on the environment in which you live; if its dry and warm outside, you probably will have few humidity issues).

When the level of humidity gets too high it needs to be removed with either a vent fan or a dehumidifier. The most common problem for most growers is finding the fine balance between exhausting moist air, enriching a room and keeping the temperature at the right level. If this is done incorrectly, CO2 will be exhausted with the air and plants will not get the benefit of the CO2 enrichment. There are many solutions to this conundrum and we will tell you two of our personal favorites. Feel free to modify these examples to fit your needs.

1. If you are using a CO2 emitter system, we suggest use of the Fuzzy Lgoic CO2 Controller from C.A.P.. It is very affordable, easy to use and extremely efficient. It will turn CO2 enrichment on and off at predetermined intervals, based on basic information you provide. (Room dimensions, desired ppm, output level of emitter) It does all the calculations for you and creates a CO2 on/off schedule coupled together with vent fan control for airing out the room. It will turn the CO2 OFF before it turns the vent fan ON and vice-versa. It comes standard with a photosensor which ensures CO2 will be turned off in the dark period when plants are unable to use it anyway.

2. For larger situations when a CO2 generator is employed, heat and humidity are even more of an issue. In this type of growing situation, we highly recommend the grower invest in the CDMC Package from Green Air, as well as a temperature/humidity controller. For a detailed explanation of how this works, click on the two product links above or click here to see how they work together.

To get a true reading of the conditions your plants are experiencing, we suggest using an indoor/outdoor thermometer-hygrometer. The extended sensor allows for placement at the plant tops where temp and humidity reading really matter. If any automated controllers such as thermostats (for example the TEMP-DNe ) or humidistats (like the HUM-1are being used,, the set points can be adjusted to compensate for the difference between ambient and plant level conditions.  A circulatory fan can also be set up to blow across plant tops, thereby removing hot air.

Is there a simple and easy way to cool my grow space?
For cooling, we suggest using a vent fan and coupling it together with a thermostat like the TMP-DNe. When temperatures get too high, the Tempstat will turn the vent fan on until the temperature drops below your chosen set point.

In most indoor environments, lighting is the major source of heat. Air cooling your lights is another possible solution. Most horizontal reflectors can be easily converted to air cooling by using a glass lens, the correct duct flanges, and vent ducting to a good exhaust fan.