Ventilation for marijuana grow rooms

How to correctly vent a cannabis indoor growing space?

Just like the lighting system or the nutrient solution, a correct ventilation is one of the most important parameters to take into account when growing marijuana indoors. A proper air ventilation allows the plants to perform all the needed gas exchanges, along with evacuating the heat produced by the lamps, achieving a better climate control and thus growing stronger plants.

Cannabis plants need proper ventilation

Indoor cannabis growroom

The ventilation systems normally used are composed of, at least,  two or three complementary elements: the air extractor, an interior fan that moves the air of the growing space and, in most cases, an intractor fan.

Which extractor fan do I need for my cannabis growing space?

The extractor fan is the key element of any air ventilation system, as it renews the air and regulates the climate of the growroom.

The needed extraction power depends on both the growing space and the lighting system used. The more light output we use, the more potent the extractor fan must be (this works also for the dimensions of our growing space). It’s all about perfectly matching the operation of this devices.

There are several rules to calculate the power of the extractor in relation to the available space, but none of them takes into account all the different factors: light output used, volume of the growing space and outdoor temperature.

Extractor fans

Which extractor do I need for my growing space?

In this table you can see which extractor should be used according to the growing area and the lighting system.

It is important to distinguish between conventional inline extractors – that are actually fans with blades – and industrial fans (RVK, Prima Klima ) which are industrial turbines much more efficient than the former. The difference in the airflow capacity (m3/h) between these two types of fans is enormous!

In practice, inline fans should only be used when growing with energy-saving lamps and perhaps also as air intractors, as we’ll see next.

If you are using HM or HPS bulbs, industrial  extractors (RVK, Prima Klima) are highly recommended. This type of extractor also allow to attach carbon filters to remove indiscreet odours from the plants.

The air intraction system of a cannabis growroom

Intractor fan

Intractor fan

In smaller spaces, the intractor fan may not be necessary if we have a good extraction system (RVK, Prima Klima). Indeed, thanks to the effect of the pressure, the air will passively enter the growing tent through the holes on its sides (to avoid light from the outside entering inside the tent, just place a piece of bent air duct in the intraction hole).

Of course, using an intractor fan is recommended:

  • To renew the plants environment with fresh air from another room or the outside, improving the climate of our growroom.
  • To limit the air pressure caused by the extractor, that tends to “vacuum”the walls of the growing tent, thus reducing the available space.

In all cases, the airflow capacity of the intractor must always be lower than the extractor capacity, specially when using carbon filters (thanks to the pressure all the odorous air passes through the filter). Generally, a simple inline fan will work perfectly as intractor.

Using cooltubes in indoor growing tents

Cooltube system

Cooltubes reduce the heat generated by the bulbs

Cooltubes are very efficient devices to lower the temperature of the growing space. With this system, some of the heat produced by the bulb is evacuated by the extractor fan to the outside.

By contrast, cooltube reflectors have a major disadvantage regarding the light output, and should only be used in case of need (temperatures higher than 28 degrees celsius) since the yields are slighty lower with this devices.

Indeed, the glass of the cooltube absorbs approximately 10% of the emitted light, even more if it is not perfectly clean. This loss is even larger regarding the light that reflects on the reflector, since it will have to pass three times through the glass before reaching the plants! Finally, the reflector attached to the cooltube is usually smaller than classic ones.

Some growers think that cooltubes are more efficient since they allow them to place the bulbs much closer to the tops of their plants, but they shouldn’t forget that the closer the bulb is to the plants, the smaller will be the area covered by the lamp. Placing them too close to the plants may cause that only the plants directly below the bulb will benefit from it, while the others may receive less light.

Which fan should I use inside my growing space?

The interior fan is a complementary piece of the extractor fan. While it is not a very efficient tool to decrease the temperature, it prevents air stratification inside the growing tent.

The interior fan is important specially for the health of the plants, since it acts as the wind does outdoors and causes:

  • Stronger branches and stems, which become more resistant and capable of supporting the weight of the buds at the end of the flowering stage.
  • Better air renewal inside the growing space, enhancing gas exchange.
  • Decreased relative humidity levels, with less diseases and pests.

The most common fans for growing tents are those usually used at home during summer. An oscillating fan with grid is much more useful than a non-oscillating one, which blows in a single direction. Most growers use one oscillating fan for each square meter.

Clip fan attached to reflector

Clip fan attached to reflector

There are other interesting fans for indoor cannabis growing; some of them can be screwed to the wall, others may have a pedestal, etc. Honeywell offers a model which can be directed upwards or downwards, as well as a double-blade fan which can be used to ventilate two different growing spaces.

Another interesting option is using clip fans , which save space and are very practical. We can easily fix them to the growing tent bars, or place them among our plants.

Many growers use the excellent Adjust A Wings reflectors with these type of fans fixed right in front of the bulb, thus preventing the formation of hot spots under the lamps like a cooltube would do, but without any kind of light waste!

It is important to use the correct fan size in relation to the size of our plants. Direct ventilation on seedlings and young cuttings is not advisable, since it could de-hydrate the tender and fragile foliage. During the first 15 days of life of the plant, we can either not use any interior fan or use it indirectly (blowing towards  the bulb or a growing tent wall). Later on, as plants grow bigger, we will also need bigger fans to move the air of the growing space. One of the best options is using fans with speed control systems.

The ventilation cycle of the growing tent

 When the lighting system of our growroom is on, every component of the air renewal system should be working with enough power to efficiently control the climate (26 degrees celsius should be the highest temperature during this period).

Ventilation is crucial for best results

Properly ventilated marijuana plants

When the lamps are off and our plants have their night period, we can decrease the airflow since there won’t be any need to reduce the temperature produced by the bulbs and the plants need less air renewal during this period. To do so, we can either reduce the power of the extractor fan using any kind of controller, or use timers to reduce the operating time of the fans, for example using them 15 minutes every hour.

Never stop the air extraction system completely for some hours, since plants always need a minimum air renewal to ensure a correct respiration.

The end of flowering is another crucial stage; decreasing the power of the air renewal system during this period will surely promote mold growth. During this stage, we recommend to use all fans and extractors at full power, 24 hours a day.

How to reduce the noise generated by the ventilation system?

Soundproof cases effectively reduce the noise generated by the extractor fans

Soundproof cases effectively reduce the noise generated by the extractor fans

Sometimes, the noise produced by these systems may be an issue for certain growers. Luckily, there are several ways to reduce this noise quickly and effectively:

  • Using soundproof air ducts in both the air intake and outtake.
  • Using a controller with thermostat or GSE,Evolution… climate controllers.
  • Isolating the RVK, Prima Klima… extractor fan wrapping it with any soundproof material.
  • Ensamlbing a wooden/metallic soundproof case
  • Using carbon filters lessen a bit the noise generated by the airflow.

How to prevent cannabis smell

The easiest and most efficient way to avoid marijuana smell in indoor growrooms is using active carbon filters . These have to be attached to RVK or Prima Klima extractors (or any other fan of this kind), using either joints/clamps or aluminium adhesive tape.

Active carbon filter attached to extraction fan

Activated carbon filters attached to extraction fans eliminate odours from our plants

Their capacity must match the airflow power of the extractor fan. We have some examples here:

  • RVK A1 100mm 160m3/h extractor fan = 100mm 225m3/h carbon filter
  • RVK A1 125mm 225m3/h extractor fan = 125mm 300m3/h carbon filter
  • RVK L1 125mm 325m3/h extractor fan = 125mm 300m3/h carbon filter
  • Prima Klima 125mm 203/360m3/h extractor fan = 125mm 450m3/h carbon filter
  • RVK A1 150mm 425m3/h extractor fan = 150mm 400m3/h carbon filter
  • RVK L1 150mm 680m3/h extractor fan = 150mm 650m3/h carbon filter
  • RVK A1 200mm 750m3/h extractor fan = 200mm 760m3/h carbon filter
  • RVK A1 315mm 1350m3/h extractor fan = 315mm 1200m3/h carbon filter

If, for any reason, you can’t or don’t want to use this filters, there are a couple of options:

  • Placing an ozonizer inside the room where you have your growing tent (do not place it directly inside the growing space since ozone is toxic for plants).
  • Using anti-odour gel , which has to be replaced often.

We hope we helped you enhancing the ventilation system of your growing space with these tips. Have a nice harvest!!

January 29, 2015 | Indoor marijuana growing
18 Comments


18 comments on “Ventilation for marijuana grow rooms

  1. Papa Indica

    Something to keep in mind with extractor, or intractor, fans is that they pull air better than they push air. Mine are set up so that the fan is at the end of the line, that way there is nothing for the fan to push air through. I have ducting connected to my reflector that runs up to my extractor fan which is at the outside of the tent, (I don’t bother with carbon filters, I like smelling weed). I use a large, enclosed reflector, it gives far better light coverage than the cool tube style, while having the same advantage of the heat being pulled out directly from the source. While the glass MAY have a negative effect, you’d be hard pressed to find it looking at my plants. Anyone who’s ever looked at my grow in full bloom would argue that the glass didn’t effect me one bit.
    I’m using a six inch extractor, a four inch intractor, and I have a Honeywell fan sitting right in the middle pointing straight up. With it pointing up, it hits the bottom of my reflector which helps it circulate back down and provides nice airflow sufficient to keep the leaves fluttering. Which is really all you want, enough to keep the leaves fluttering.

  2. Kevin

    Hello. A little advice please on how to read the formulas concerning witch size extractor for the size of the space and wattage of the bulbs.

    1. Dani Alchimia Post author

      Hi Kevin,

      The wattage of the bulbs and the available space are the main factors that determine what type of extractor should be used. On the left column you have different grow tent dimensions, while on the right you have different lighting equipments. For example, if you’re using a 1,2m2 grow tent and a 600W HPS bulb, you’d need a 425m3/h extractor fan. Imagine that you have more space (1,4 x 1,4 metres) and want to use a 1000W HPS lamp; you’d then need a 680m3/h fan. Finally, if you have a small grow tent (80 x 80 cm), a 225m3/h fan would be enough for a 250W HPS.

      Hope it helped!

  3. neorabbit

    Hi,

    I need to ventilate a grow room of 4m x 4m x 3m (exactly 42m3).
    Someone told me that I need to calculate:

    Volume x 60 minutes x 1,5 for adjusting loss of carbon filter and noise.

    So for me it should be 42 x 60 x 1,5 = 3780m3/h
    This seems to much for me…
    Could you advice me??
    Best regards to all the Alchimia team, 😉

    1. Dani Alchimia Post author

      Hi neorabbit,

      Sorry for the late reply, I’ve been in Vancouver at the LIFT Expo.

      It depends on several factors like number and type of lights, outside temperature, total volume, capacity of the air intake, carbon filters, etc. Generally, for a room like yours a 200mm/1100m3/h extractor fan should be ok. If you want to be sure you can also choose a 315mm/1420m3/h fan.

      Thanks for your confidence!

  4. JOAO FARIA

    when cannabis plants start need fan on?

    1. Dani Alchimia Post author

      Hi JOAO,

      Plants love proper air circulation around them, so the best option is using the fan from the very first day.

      Hope it helped!

  5. Darren

    Would a standard kitchen/bathroom wall extractor added to a grow cupboard work well for smell and ventilation if there is a hole on the wall that leads outside to put the fan in? Or would I need a carbon filter setup? Any help would be great thanks

    1. Dani Alchimia Post author

      Hi Darren,

      That setup would be ok, although you may need a more potent air extractor if you use HPS lamps or outside temperatures are high. That’d also depend on the dimensions of your closet. Cannabis plants in full bloom are extremely smelly, so using carbon filters is always advised unless you live in a truly isolated area.

      Hope it helped!

  6. Justin williams

    I have a 48x24x60 tent and just got a 6 inch visco fan for sucking air out of the tent, I’m now looking for a fan to pull air into the tent. What size fan would you recommend ?

    1. Dani Alchimia Post author

      Hi Justin,

      The only thing that you must keep in mind is that your new intake fan must be of lower capacity than the extraction fan you’re already using. In this way, you’ll keep the negative pressure inside the tent. A 3-4 inch fan will probably do.

      Hope it helped!

  7. len price

    Dani: I live in B.C. There is a Licensed Gro-Operation next door to me which is classed as Agri. They do not mix we have never spoken to them so I have no problem as far as being neighbours. My problem stems from the 2 huge Greenhouses which have been erected in the last 9 months. They have two huge and I mean huge (Jet Plane size) fans pointing right at us. The smell is overwhelming and pungent because of the volume they are venting. Is there any recourse I can take.? My health is not good and we are unable to sit out on our deck used to be in the evening but now through parts of the day. Can this establishment be checked and by whom to see whether the problem can be eliminated. I don’t care what business they are in but I do care when it is affecting me and my wife.
    Thank you

    1. Dani Alchimia Post author

      Hi Pepi,

      I’m sorry about your problem, it must not be pleasant at all to have these type of fans pointing at your house. Unfortunately, I don’t think there’s much you can do but telling them about it (perhaps they’re good and sympathetic people and they understand) or complaining to the corresponding institution/agency. There must be some type of smell/sound limit for these greenhouses, and they do have the needed materials to eliminate any odour coming from their plants (carbon filters).

      I really hope you can solve your problem!

      Best!

  8. Pepi

    Hi Dani

    Please use the name Pepi instead of my name which I gave you by mistake regarding my next door venting system of 2 huge greenhouses.

  9. Billybob

    I have a 10ft x 10f x 8ft grow room do I need ducting to move air In an out what’s my cheaper route to get good ventilation

    1. Tim Alchimia

      Hi Billybob, thanks for your question. Yes, you’ll need to install some kind of air extraction system, but what type will depend on the kind of lights you’re going to use and the temperature at the time of year you’re growing, obviously an autumn grow in Alaska won’t need the same amount of ventilation as a Summer-time grow in Arizona!

      Your grow space is around 21 cubic metres, which converts to roughly 760 cubic feet. For the proper ventilation the air in the room needs to be changed every 3 minutes, which means you’ll need a fan with a minimum capacity of around 250 CFM and all the necessary ducting to extract the air to the exterior.

      As for a cheaper route, I’m not sure if that would be false economy in the long run, it’d be heartbreaking to spend all that time setting up the grow room, caring for the plants to then have the harvest ruined due to poor air renewal and circulation. I’d recommend getting the best ventilation system your budget will allow, it’s a great investment for the future.

      All the best and happy growing!

  10. Rockstar

    Thank you for your amazing information

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