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Try the “closed system” for easy grow-room setup
By Dr. Who

There are many ways to set up your new grow room. You might have gained your knowledge by talk



Try the “closed system” for easy grow-room setup

By Dr. Who

There are many ways to set up your new grow room. You might have gained your knowledge by talking to your friends, reading magazines, watching videos, etc. You need to be able to sift through all of this information and find the way that is right for you. As a grower with more than 20 years of experience, I have set up many different grow rooms. Over the years, I have come to one conclusion: the simpler, the better. I will explain to you the easiest method that I have come across—the “closed system.”

The “closed system” means that there is no air exchange between your grow room and the outside air. This system has many advantages. The first is that no complicated ventilation is required. Odors are much easier to control. Pest infestation can be controlled easily. The environment is also easier to control. Some of the disadvantages are that you need to dedicate an entire room to the project. Another is the start-up cost. Don’t be dismayed—the costs are not that much more than an open system, and will save you money and hassles in the long run.

First, you need to choose your area. A bedroom is ideal. If the bedroom also has a bathroom, that is even better. Second, you need to choose your lighting. A 1,000-watt high-pressure sodium lighting system will cover about a 5-foot by 5-foot area. You can normally put two or three lights in a bedroom without too much trouble. Third, you need to choose your growing method, either hydroponics or soil.

The next crucial item that is needed is an air conditioner. You should find an A/C that is sufficient to cool the room with the lights running. Finally, you need a CO2 supplementation system. You can use either a CO2 generator, which makes CO2 by burning propane or natural gas, or bottled CO2 with a flow-controlled regulator. Either method requires a CO2 monitor to control the levels of CO2 in your room.

The A/C should be a manual unit (not digital) so that your A/C will continue running even after a power failure. Each 1,000-watt light produces about 3,000 BTUs of heat. You should calculate about 4,500 BTUs per light to allow the unit to cycle so that it does not stay on all of the time. You can either use either a window unit, or a portable one. Beware of cheap portable A/Cs, which do not really put out the BTUs that are claimed. Use a name-brand unit.

Now that you have collected all of your equipment, you should hang your lights and install your A/C and CO2 system. To test the system, set the A/C to about 80 degrees Fahrenheit, turn it on to re-circulate mode (this mode does not exchange outside air with inside air). See if your room can be cooled to that temperature with the lights running.

Now, you need to check out your CO2 system. Set your CO2 controller to 1,500 ppm (parts per million). When you room hits that CO2 level, observe how long your room keeps at that level. You should go at least 15 minutes before the CO2 levels drop to 1,450 ppm. If it is less, you have an air leak. Check the gap on the door. Use weather stripping if necessary. Check to see of the A/C register for the house A/C is closed. You may want to tape it up to prevent any air being introduced into the room. Remember that any air that is introduced into the room causes air to flow out of the room. Your CO2 and A/C will be much less effective if the room is not “tight,” and you will be forcing odors out of the room.

One more piece of equipment that you might need is a dehumidifier. Humidity levels tend to rise quite a bit at night. You should try to keep your room at about 50-percent humidity at all times to prevent mold and to keep the stomas (the CO2 collectors on the undersides of the leaves) open, leading to better growth rates.

DR. WHO is a Southern California expert in plant cultivation. Reach him at

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