Why airflow is so important for your grow room

Why airflow is so important for your grow room … and how to get good ventilation Airflow is vital when growing plants. It has 2 main functions:

  1. Good airflow removes stale air with depleted co2 content and replaces it with new co2 enriched air.
  2. It helps control the heat and temperature levels in the grow room

Over at growersguidetocannabis.com’s live chat we’re amazed by the number of times (daily!) someone asks us: do I really need an extractor for my grow room? New growers planning their first indoor cannabis grow room get that they need lights, nutes, a grow system: but all too often see ventilation as an optional extra they can exclude from their list if budget is tight. This is not the case:  

good ventilation is as important to a successful cannabis grow as lighting is

Without a decent air flow through your grow room, CO2 levels will become depleted, the stomata on plant leaves become unable to transpire properly, heat levels increase and humidity falls. Before very long the plants start to suffocate. Not what you had in mind!  
The optimum temperature range for growing cannabis indoors is between 20-28`C with a sweet spot of 26 C. You can go outside this range a little without ill effects but anything much above 30`c and your yield lessens.  Whenever you use HID lighting you WILL need to extract excess heat from your grow area.   What do I need to create good ventilation in my grow room? Sorting out good airflow through your grow room can be slightly complicated especially to a new grower. Here we run through the basics: Essential ventilation equipment: 1. An extractor (plus ducting, connectors) The mainstay of your ventilation system, an extractor pulls heat and stale air from your grow room. Normally you would place at the top of your tent / room and vent to the outside.  The most common type used in the grow room is a powerful “inline” mounted fan which is designed for high performance and relatively low noise. The size of the fan is described by the duct diameter size (e.g. 4” or 100mm), and its always best to buy matching ducting (tubing) filters etc rather than use reducers to adjust mismatched systems. For more information on how to determine the size of extractor you need please read here: Ventilation FAQ Always upsize the fan needed if unsure which one best fits your room size.

Vents TT Extractors

The basic budget extractor. Features two speed single-phase motors and thermal overload protection.  The plastic flanges at either end make it easier to add ducting etc to the fan. They will do the job well enough, although may lack the same power/air movement capacity as the same diameter extractor of better quality and probably will not last as long. That said, as long as you bear these facts in mind, they are a good piece of kit for the money.

Systemair RVK Extractors

Made in Germany, these are the standard extractors many experienced growers use.  Built with quality materials, they are quiet running and powerful.


When setting up your airflow system its important to realize a simple fact: the more bends (excess piping) your system has, the greater resistance to airflow. Smooth out and stretch the ducting to allow the extractor to pull the air through easily. THAT SAID, between the extractor and the outside area it is good to make at least one 90` bend to lightproof the room. 2. Timer / Controller You don’t want your extractor running continuously: doing so will add to your running costs and also lead to low humidity levels. There are three ways to control your extraction rates: 1) if you are on a budget you can use a simple timer (such as the one below). Check your humidity and temperature gauge regularly and adjust the timings your extractor comes on for until these levels are correct for your stage of growth. 2) Invest in a thermostatically controlled extractor. This has the timer built in and will switch on and off according to temperature. Primaklima extractors 3) Buy a speed controller specifically designed for your extraction. Speed controller.   Circulating Air Another important factor in airflow in the grow room is the need to circulate air within the room itself. As Carbon dioxide is heavier than air you need to use an oscillating fan to keep air moving within the room: it also stops heat pockets building up. An additional benefit is that airflow strengthens the stems of the plant to allow big bud production. Many growers use both a stand up oscillating fan and a small clipon fan to make sure of good air movement. Intake Fan Small grow areas can use passive extraction but if you are growing in a larger area using multiple lights then a small intake fan to draw fresh air into the room is recommended.  Draw your intake air from another room in the house (rather than outdoors) as temperature levels inside are more stable and there is less risk of pests entering your room.

Helical In-Line Extractor T-100 (Vents)

Economic fan that works well as an intake fan but lacks the power for extraction.


Unless you are lucky enough to live in rare isolation (and even then you need to remember the occasional visitor like the electricity meter man) you need to plan how to deal with the smell produced by your plants. There are 3 main ways people get caught for growing:

  • heat signatures large increase in power consumption combined with telltale “peaks” as lights power on
  • smell
  • blabbermouths: those who talk too much

Even in vegetative stage many cannabis strains produce a distinctive odour. And once they start flowering your tent full of luscious budding ladies will emanate a full-nosed fragrence that seeps out of the tent and into the air around. For security’s sake you really need to get on top of odour control and stop this happening! There are a few options available in odour control management but the mainstay has to be the carbon filter (or scrubber).

Carbon Filters

Carbon filters attach to the extractor (hence the inclusion in the ventilation section). As the smelly air is pulled out of the grow area by the extractor it is pushed through the carbon filter, a metal hole punched tube which passes the air through activated carbon. These carbon particles neutralise the smell thus effectively removing it before it reaches the outer environment.

Which carbon filter should you buy?

As always the more you spend the better product you can get. With something as important as odour control (see security risks above) its important to overbuy rather than underbuy. That said, think about the size of your grow and the type of plants you are likely to use. A smaller grow tent with 3 small Northern Lights plants will put out a lot less smell than a 1.2 x 1.2 growing Kaliman’s Cheese #1. Just two kilos of charcoal granulated carbon granules contains within its porous structure a surface area of approximately 100 acres, making it still to this day the best media for both water purification and air purifying systems. Don’t forget to match your carbon filter neck size to the size of your extractor 🙂

So to sum up: good ventilation is essential to a successful grow room. Your extractor controls heat levels and ensures fresh air is available for your plants. Oscillating fans reduce hot spots, circulate carbon dioxide and strengthen plant stems. A humidity / temperature gauge gives you knowledge about the climate ranges within your area whilst a carbon filter attached to your extraction is the best way to eliminate smells.


Some of our ventilation products


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