# Marijuana Cultivation/Fundamentals/Ventilation and Odor Control
### Ventilation and Odor Control

Ventilation is absolutely essential to plant health. Plants absorb CO2 and release oxygen. The roots in turn require oxygen so both must be present in your grow environment. Additionally odor control will be very important. Marijuana has a pungent odor and some strains can be smelled for miles without some form of odor control.

#### Negative Ion Generation

Negative ion generators can help with odor control problems. These machines will use a negative charge to attract positively charged particles in the air. These are best purchased off the shelf but you do need to know that you shouldn't actually put the generator in the room with the Plants. They are said to interfere with the taste, odor, and even potency of the end product.

#### Ozone Generators

Ozone (O3) is what gives the air a fresh smell after a thunderstorm. Ozone oxidizes organic particles in the air but in high concentrations can irritate your lungs. For this reason ozone generators are typically put on the timer with on and off cycles to allow the system to output just enough ozone to control the odor.
These generators come in two basic varieties, corona discharge and uv generation. Since uv generators require longer exposure to the air the corona discharge systems are probably more sensible for most gardeners. There are plans online to make corona discharge units with neon sign transformers. This is definitely NOT recommended, these devices are a severe fire and electrocution hazard that will not be properly isolated and housed and will be placed in a wet environment. It is probably a safer and more effective idea to simply purchase a small used unit.

#### Odor Neutralizers and Masking Agents

One common technique for a small scale closet grow operation to build an odor remover bucket. Simply drill 1/2 inch holes around the top of a 5 gallon bucket. Fill the bucket with perlite or absorbent crystals and then add an odor neutralizer or masking agent chemical.
Odor neutralizing agents such as ONA are definitely more effective than those that merely mask odors.

#### Active Carbon Filtration

This technique involves forcing exhaust air through active carbon in order to filter out odors. This method is highly effective and very popular and can also be used in combination with the other methods. These filters can be purchased or you can find plans to construct them online.
Ideally, you would use your exhaust fan to pull the air through the filter rather than push air through it.

#### Intake and Exhaust

Unless you are adding CO2 you should make sure that you have a highly effective exhaust system. You will want to make sure your exhaust fan is rated for high CFM under pressure. All fans will have a CFM rating, this rating is how many cubic feet of atmosphere the fan moves per minute. Your exhaust fan should be capable of evacuating your grow room at least once every five minutes. Multiply the width, height, and depth of your room to determine the total cubic feet, divide this number by five and you will have the minimum CFM fan rating needed. Of course this assumes the fan maintains its CFM under pressure and actually performs to specifications. In practice this doesn't happen. It is best to overshoot this rating as much as your budget will allow. Even if your fan does perform to specifications pulling more air through will help keep the temperature of the room down and exhaust the heat from powerful fans.
Generally squirrel cage and duct fans are used for exhaust systems. These fans can be connected to 4 inch and 6 inch flexible ducting that can be used to route the air where you want it and to pull air through a carbon filter.
In addition to your exhaust system you will need an air intake. For many systems a passive intake is used, simply providing a channel for fresh air to enter the grow room to replace the air being exhausted. For a larger area or longer intake line you may need an active intake. Providing an active intake relieves pressure to allow the exhaust and intake to share the workload of air exchange. Otherwise the exhaust fan must provide the force required to pull air into the room as well as the force required to exhaust.

#### CO2 Supplementation

CO2 Supplementation yields dramatically larger flowers than growing without adding CO2. The idea is to replicate earlier geological conditions when atmospheric carbon dioxide levels were higher and plants grew far larger than they do today. The ideal level of CO2 is between 1500-2000 ppm. There are many ways to add this CO2. CO2 moves very easily and weighs more than oxygen. Because of this you will want fans to be off during the period in which you are supplementing CO2. Because plants only utilize CO2 for photosynthesis you will only need to supplement during the lights on period.

##### Fermentation

This is done by fermenting sugars with yeast. Sometimes even basic sugar and water is used for this purpose. Others use a more sophisticated blend with nutrients for the yeast. You will need to use an airlock (tubing coming out of a sealed fermentation vessel or jug and placed in a cup of water so the CO2 has to bubble out through the water will work). This method is very cheap and easy to setup but while every bit helps this will not raise your CO2 levels to the ideal 1500-2000 ppm.

##### Dry Ice

You can generate CO2 by simply melting dry ice (which is frozen CO2) but it is difficult to control the speed of release to precisely control the CO2 levels. Additionally you will need to add ice each day and the ice can not be kept in your freezer.

##### Vinegar and Baking Soda

When vinegar and baking soda react they release CO2. You can produce CO2 at a controlled rate by utilizing a drip system.

##### Propane Burners

Propane burners generate lots of CO2 and can be controlled but they also generate lots of heat that must be exhausted.

##### Stored CO2 Canisters

These can be purchased with cash at any gas supply shop. This is the least expensive and most controlled way to supply CO2. The downside is that there is a high up front cost and a few calculations are required to determine how to setup the system and output CO2 at the proper rate.
The details of the setup will vary based on your equipment but there are a few basic components you will need to use this method. The first is a tank. Tanks must be refitted with new seals periodically. Generally a gas supply will exchange your canister with another that has a similar amount of time left on it rather than fill the canister on the spot. In addition to the canister itself you will need a solenoid switch to allow you to use a timer to control when the tank releases gas and when it does not. A regulator is needed to regulate the pressure to a lower and fixed pressure that won't damage your other equipment. To the output of the regulator you will need a flow meter with needle valve. Usually this will consist of a tube with increment markings and a little ball that raises to show you how much CO2 is flowing through the flowmeter. This allows you to fine tune the output of your CO2 system. Finally you will need plastic tubing with holes in it in order to actually distribute the CO2 around the grow area. Remember CO2 is heavier than air and will fall downward when released out of the tube. This means you should position the tubing above your plants.
You can purchase all of these components aside from the canister as kits sold for hydroponics. Follow the directions that come with the kit to set your timer, flowmeter, and regulator.