Q: Do I really need extractor fans in my grow room?

A: Ventilation is often overlooked when building an indoor grow room and is one of the most important things to get right. Inadequate ventilation is the cause of the majority of problems we see.

A drafty loft or leaving a window open simply won’t do! Extractor fans are to needed to control temperature and humidity but also to supply the plants with the carbon dioxide they need to grow.

No air = no carbon dioxide = no growth.

One of the greatest pieces of advice to any new grower is to get your ventilation system right. Good ventilation is the key to healthy, fast growing and high yielding plants. Poor ventilation is the key to an unhappy and unsuccessful time at growing plants!

Q: What size extractor fans do I need?

Below are two ways you can work out the size of extractor fans you will need in your grow room.

1. This method is based on the volume of the grow area and is perfectly suitable for small grow rooms.

First calculate the size of the room in cubic meters (m3): Length x Width x Height in meters = size of room in cubic meters.

Then multiply the total m3 by 25 to give you the air exchange needed in one hour.

Add 30% to this figure to allow for the inefficiency created by using carbon filters and lengths of ducting and the figure you will have is the air exchange rate needed in m3/hour for your grow area.

Because all extractors are sold with a m3/hour air exchange rate, it is a simple matter to select the correct size fan(s) you will need. For example, if you have calculated the air exchange rate needed is 450m3/hour then this could be achieved by using one exhaust fan rated to 450m3/hour or by using two fans, one for input and one for exhaust that together total this amount. If you use two fans (recommended) make sure that the exhaust fan is approximately 70% larger than the input fan.

2. This formula is used by commercial growers and is based on the number of lights used. This is recommended for medium to large sized grow rooms and guarantees the control of temperature regardless of the number of lights being used.

Extraction:

Take into account at least 200m3 of exhaust for each 400w lamp
Take into account at least 300m3 of exhaust for each 600w lamp

Add approximately 30% more exhaust to this to allow for the inefficiency created by carbon filters and lengths of ducting.

Intake:

Intake should be approximately one third to one half of the volume of the exhaust. (If your extractor is 1000m3 per hour or less, use approximately one third of its volume for input. if your extractor is over 1000m3 per hour, use one half of its volume as input)

Example 1: A grow room with 5 x 600w lamps would be 5 x 300m3 = 1500m3 of exhaust. Add around 30% to this (approx 500m3), and you will need 2000m3 of extraction. The size of the intake fan should be approximately half of this, so about 1000m3.

Example 2: A grow room with 2 x 600w lamps would be 2 x 300m3 = 600m3 of exhaust. Add around 30% to this (approx 180m3), and you will need 780m3 of extraction. The size of the intake fan should be approximately one third of this, so about 260m3.

Q: How do I set up a ventilation system?

A: The theory is simple. Hot air rises so your exhaust fan should be situated at the highest point of the grow room and the intake should be situated at the lowest, most opposite point. Air should come in from below and make its journey up through the grow room and through the plants, supplying them with what they need. The air then moves out through the extraction from above taking away with it excess temperature and humidity. You must be careful to avoid what is known as a ‘laminar flow,’ this is where air is drawn in through one vent and out through another without moving through the plants. You may find it helpful to imagine that you can see the air flow as little arrows making their journey through the room. There should be no stagnant areas in the room, the air should always be moving. Oscillating fans are essential to move the air around as it makes it journey. Take care not to bash plants around with oscillating fans; the idea is to move the air around the plants rather than moving the plants themselves. When you look into your grow room you should see the leaves gently shimmering as the air moves through them. They should not look like they are in force 9 gales.

Q: Do I need a separate fan for the intake?

A: It is advisable to have a separate intake fan although you can use a passive inlet. This needs to be a vent hole at least the same size as the size of the extractor you are using to draw air out of the room, for example, if you are using a 200mm extractor then the size of the inlet hole should be at least 200mm. This can be one hole or several providing the total open area equals at least 200mm. In practice we recommend the inlet hole to be approximately 20% larger than the exhaust, this reduces drag and allows the extractor to work more efficiently. Providing that the rest of the room is sealed, the volume of air the extractor is pulling out will now be pulled in through the passive inlet.

A separate intake fan that is one third to one half of the volume of the extraction fan is much more efficient and is what we recommend. It allows better control of temperature and humidity, creates a negative air pressure within the room that is good for plants and prevents smells escaping back through the ventilation system, and because the extractors are not working so hard you will find they makes less noise and last longer. Also the size of the hole needed to fit an input fan into the room needn’t be as large if using a passive inlet.

Q: How much noise do these fans make?

A: The extractors we use for hydroponics are chosen because they are capable of moving large amounts of air in extreme environmental conditions. They are also capable of pushing or pulling air through lengths of ducting and are powerful enough to draw air through filters that remove smell. If the extractor fan you need for your grow room is only small (100mm – 125mm) then you will find them very quiet indeed but fans larger than this can get noisy. The noise that the motors in these fans make when you consider the work that they are doing is incredibly low, it tends to be the sound of the large volumes of air moving through them that makes the noise. With correct installation this noise can be reduced significantly. If noise is an issue then the best piece of advice is to purchase a fan that is larger than you actually need and turn it down. A large extractor turned down will make considerably less noise than a smaller fan running at full speed and will still be moving the same amount of air, if not more. Without exception, the quietest grow rooms will have the largest extractors running at lowered speed. Also make sure that all ducting is kept as short and as straight as possible and avoid bends in the ducting as these will create drag that in turn creates noise as the air moves through. As noise is created by vibrations, anything you can do to reduce vibration will help to reduce noise. Using acoustic fans, silencers and insulated ducting is a good idea, and use pressed bends if you need to turn corners with your ducting as these will also help to reduce noise and keep the ventilation system working efficiently. We also recommend using a decent fan controller like the SPC, Fan Controller or Twin Fan Controller. These controllers will see that your fans only run as fast as needed to maintain a set temperature. This keeps noise down to a minimum.

Fan Controller: http://progrow.co.uk/acatalog/info_4555.html
Twin Fan controller: http://progrow.co.uk/acatalog/info_4925.html
SPC Controller: http://progrow.co.uk/acatalog/info_4520.html
Ventilation supplies: http://progrow.co.uk/acatalog/fans-filters-ducting.html

Q: Do I need to use my extractor fans at night?

A: In theory the answer here is no as plants do not require Co2 at night and there is no heat from the lamps to deal with. However, humidity causes problems at night and so do smells that start to escape back through the vents when the extraction system goes off. The best approach is keeping the extraction system running during the lights off period but at a lowered amount. Using a fan controller will do this automatically for you.

Here is a link to a suitable controller for a single extractor: http://progrow.co.uk/acatalog/info_4555.html

Here is a link to a Twin Fan controller: http://progrow.co.uk/acatalog/info_4520.html

Q: How do I measure temperature and humidity?

A: Using a hygrometer/thermometer. It is a small instrument used to read both the temperature and the relative humidity of an area. They are an absolutely essential piece of equipment for the indoor grower as before you can begin to control these factors you need to know what they are! A decent meter will also have a function that records both the minimum and the maximum parameters so you can keep a close check on the history of your environment. The correct way to use one is to place it near to the plant canopy but not directly under the light. The meter should have its min/max function read and then zeroed as the lights switch on at the beginning of the daytime period and then again as the lights switch off at the beginning of the night time period. This way you will begin to build a clear profile of the differences in temperature and humidity for both the day time (lights on) and night time (lights off) period. This must be done regularly as these parameters will change as the plants grow and as the seasons change outside. With this information you can alter the environment in your grow room as necessary.

Here is a link to a suitable hygrometer/thermometer: http://progrow.co.uk/acatalog/info_2786.html

Q: What is the ideal temperature?

A: The ideal temperature is around 28 degrees C in the vegetative stage and a couple of degrees lower in flower. It is also better to have a dark period temperature lower than the light period temperature, this is essential for correct flower maturation. Plants regulate their growth depending on environmental restrictions so keeping the growing temperature steady and free from major fluctuations will lead to superb growth.

Temperature can be controlled by using a Fan Controller. These will automatically adjust the speed of the fans to maintain a set temperature.

If you are using a passive inlet, use this controller:http://progrow.co.uk/acatalog/info_4925.html

If you are using and extractor and an input fan, use this controller:http://progrow.co.uk/acatalog/info_4555.html

Q: What humidity should I maintain?

A: Using standard equipment, try to maintain humidity at around 50% in the centre of the plant canopy. 40% - 60% is ok. If you have full control over humidity we recommend around 70% during the vegetative and early flowering stage and then lowering the humidity during the latter part of flowering to around 35% - 40%.

Q: Should I use added CO2 in my grow room?

A: Raising the levels of CO2 in the grow room will increase growth rates, reduce crop times and increase yields up to 30% if used correctly. The key words here being ‘if used correctly’. The process of elevating CO2 levels to the point that true benefits can be seen requires a command over every aspect of the grow room. This means perfect lighting, perfect nutrition and perfect environmental control. If you do not have full control over these factors then adding extra CO2 is a costly an ineffective past time. If you do have the perfect room then adding extra CO2 will certainly prove beneficial and will increase production. Please feel free to contact us for help in choosing the right system for you.

Q: The exhaust from my grow room smells. Is there something I can do about it?

A: Yes. With modern equipment it is possible to remove all smells created by your grow room. The first step is to fit a carbon filter to your exhaust fan. Carbon filters will remove smells before they are exhausted to outside. A decent filter is 99% effective but they do need to be replaced/refilled after time. For smells inside the house we recommend using an ozone generator. These machines will physically remove smells by a process known as oxidation. Some care needs to be taken when using ozone as in very large concentrations it can be harmful to your lungs however the units we sell are designed for home use and do not produce enough ozone to be considered a real danger. Test kits are available to help you regulate the amount of ozone you are producing. Ozone is also an effective steriliser and will kill airborne moulds and bacteria.
You can also use a product called Ona to help target smells. Ona is a kind of jelly that comes in jars and can be used to spot treat smells.
Here is a link to Carbon Filters: http://progrow.co.uk/acatalog/carbon_fi ... ncers.html
Here is a link to Ozone Generators: http://progrow.co.uk/acatalog/info_716.html
Here is a link to Ona Gel: http://progrow.co.uk/acatalog/info_4606.html

Q: Do I put my fan and filter. Inside or outside of the grow room?
A: The fan and filter are normally placed inside of the grow room or grow tent, so the air is drawn through the filter and then the fan before leaving through some ducting to outside.
If space is an issue, this can be reversed so the fan and filter are placed outside freeing up space inside the grow room. When set up like this, air is pulled out of the grow room through some ducting by the fan located outside, the air then moves through the fan and is then pushed down some more ducting before being pushed through the filter which is on the end of the line. If you are doing it this way around it is a good idea to take the white pre filters cloth from the outside of the filter and push it inside instead, as the filter is now being used in reverse. Try to keep the fan as close to the grow room as possible and keep all lengths of ducting as short and straight as possible.
So to recap, you can either go:
Filter – Fan – Ducting – Out (recommended)
Or
Ducting – Fan – Ducting – Filter- Out