Setting up the Perfect Sealed Grow Room

Apart from a few pots, media and plants, most indoor growers will start out with a grow-tent, a grow-light and an extraction system (as comes with one of our essential grow kits). The tent provides the grow-space, the grow-light provides the light and warmth, while the extraction kit removes stale, CO2 depleted air, excess heat and odours. This "open loop" or "ventilated" type of system, as it is called, is an economical and fairly effective way to get started.

As time goes by, growers will usually make some improvements and embellishments to their grow such as with the addition of a fan speed controller, and some other handy tools.

The "open" or "ventilated" type of system described above certainly works, but it does have its disadvantages. Because the air is constantly being replaced, it can be difficult to maintain a particular relative humidity, or to increase the CO2 level in the air which can greatly increase plant growth rates. The air temperature and the relative humidity together create an effect called Vapour Pressure Deficit (or VPD for short). Getting the VPD level correct is one of the major keys to getting the most from your grow, and the CO2 level is one of the others. You can read more about VPD Here.

In warmer parts of the world, something called "closed-loop systems" have gained enormous popularity, particularly with commercial growers. Closed-loop systems involve having a completely sealed grow-room. No air is extracted out to or drawn in from outside the sealed grow-space. Instead, the temperature is kept within the right range by a heater and an air-conditioning unit. Humidity is controlled by the use of dehumidifiers and humidifiers. Plus, with no air being drawn out or in, the use of CO2 supplementation becomes well-worthwhile. CO2 levels can be supplemented with a controller, a regulator and a bottle:

Of course, air temperature, relative humidity and CO2 levels are not the only aspects of growing that are of benefit to be taken care of. Odours are generally not a problem because the room is sealed. However, for many growers, it would be wise to employ some back-up insurance in the form of an ozone generator or an "air scrubber" which can be made from a carbon filter, a duct fan and a fast clamp, just in case something goes wrong.

Plants will slowly use up the CO2 in the air. Plants respond favourably to CO2 levels at anywhere up to 3-4 times higher than is found naturally in the air around us, but as plants use up the CO2 their growth rate will actually go down. This needs to be replenished in some way and as a CO2 enrichment system is going be utilised it means that the levels can be increased to a level which maximises growth potential. With CO2 enrichment, good air circulation is an absolute must to keep the air mixed and consistent around the plant's leaves.

This type of system has a lot of advantages over an open, ventilated system. It offers the grower the ability to take tight control of temperatures & relative humidity (and therefore VPD) as well as increasing the CO2 level. The combination of CO2 supplementation and spot-on VPD can a make huge difference in plant health, growth rate and eventual yields. However, the implementation requires some care in planning and also some investment.

What you will need

First of all, of course, you will need a sealed room. For this system to be as effective as possible there should be no gaps around windows, doors... or anywhere!

Next, an air conditioning system and possibly a heating system will be required. Also, a dehumidifier should be on the list of essentials. When plants transpire, they release water into the atmosphere. In a closed loop system, the relative humidity can increase until it reaches saturation point. The VPD (drying ability of the air) will become so low that plants are almost unable to transpire. Once something called the "Dew Point" is reached, water will begin to condense out of the air onto ceilings, walls and other surfaces, particularly if they are slightly cooler than the air. A damp atmosphere is almost asking for problems with fungi and moulds too.

One of the greatest products for sealed rooms is the Opticlimate full climate control system (read more about them Here).  The Opticlimate units contain a heater, an air conditioning system and a dehumidifier all in one box. An air filter is included to protect its internals.

Opticlimate units require an electrical feed and a water feed. It also needs to have a water drainage point. However, once it is set up, the user can program in their desired target temperature and relative humidity.

As we mentioned in out article about CO2, the leaf temperature can and should be a bit higher than is usually regarded as optimum (optimum is usually about 22-24 ºC for most plants). Ideal temperatures with CO2 supplementation can be several degrees higher. At this temperature, the optimum relative humidity is higher too in order to achieve a good VPD.

Generally speaking, the amount of photosynthesis that a plant can perform is either light limited, or CO2 limited. Without CO2 supplementation, plants can utilise up to around 800 µmols/m2/sec but the law of diminishing returns really starts to kick in at around 500 µmols/m2/sec. With CO2 supplementation it is worthwhile pushing the light intensity up to 1000 µmols/m2/sec or even slightly more.

Investigating the "Hybrid" Grow Room

In many parts of the world, large sealed grow-room setups have been springing up like wildfire. There have been reports that some experienced growers begin to experience plant problems that are difficult to explain. Theoretically, the closed-loop system offers what would seem to be almost ideal grow conditions. The temperatures are bang on, the RH is bang-on, VPD is exactly where it should be, and CO2 levels are optimised. Even the addition of scrubbers (circulating the air through a carbon filter with a duct-fan attached back into the room) does not fix the problems. So, what could possibly be going wrong?

To not put too fine a point on it, no one seems to know for sure but we can make some educated guesses. Some sealed-room growers experience odd shaped or wilted leaves, and lower than expected yields. The finger of suspicion is usually pointed towards the "gassing off" of certain building materials and/or a build-up of ethylene gas which is produced by roots when they hit an obstacle. Some building materials off-gas nasties such as formaldehyde! Of course, in a sealed room, the levels of these gasses just keep on building up. Here is a list of some of the worst offending building materials for off-gassing:

  • Plastics
  • Paints, Stains and Varnishes
  • Glues, Sealants and Caulks
  • Insulation (including Fibreglass)
  • Plywood and Particle Boards
  • Carpet and Vinyl Flooring

With that suspicion in mind, some of the guys that specialise in setting up and running sealed grow rooms have come up with a solution. It simply involves employing a traditional extraction system comprised of a carbon filter and duct-fan and ducting which ducts to the outside instead of being circulated back into the room (like with a scrubber).

The idea of doing this is counter intuitive. After all, enriching the air with CO2 costs money. To suck out all that CO2 enriched air to be replaced by unenriched air seems daft, yes? However, instead of running that extraction system at a low level 24/7, growers' experimentation seems to show that it is adequate to just turn on the extraction system and replace the air in the grow-space about 2-4 times per day. That way, unwanted gasses or ethylene do not build up to plant-affecting levels, and it does not raise the cost of running CO2 enrichment by much at all. If you have a sealed room system and your plants look less than tip-top and your yields are disappointing then it may be well worth thinking about turning your sealed grow-room into a Hybrid set up.

Expert tips