Ventilation can be a relatively tricky business so we've tried to make it a bit easier with the calculators below. Basically there are two main considerations when working out how to ventilate your grow area: Air exchange and heat.
Air Exchange
Plants require Carbon Dioxide when photosynthesising during the day and Oxygen when respiring at night. If the room is still and there is no air exchange, both are used up very quickly and the plant suffocates. Moisture is also released into the air as the plants transpire and this also needs removing. The minimum amount of times a room needs to exchange air for the plant to be healthy is once every 5 minutes. Enter the dimensions of your room into the Room Fan Rating Calculator below to work out what size fan you will need to do this.
Heat
Plants grown hydroponically under indoor lighting are generally happiest at between 70 & 80 Farenheit (26-29*C). All lighting generates heat, especially HID lighting, and ventilation is required to push hot air out and pull fresh, cool air in. We recommend intake air is drawn from indoors as temperatures remain more consistent throughout the year and there is the added benefit of extra CO2 in the air from humans and other animals breathing in the house. Draw air in from as low down in the room as possible and expel air from as high as possible.
When entering the figures below, it is usual for a house to average a temperature of 65F which can be used as the Air Intake Temperature. The Ideal Extract Temperature should generally be 75F.
If you are considering a summer grow (where temperatures can exceed 75F) sometimes the best you can hope for is a 5 degree differential, e.g. an Air Intake Temperature of 80F and an Ideal Extract Temperature of 85F. Anything above this and we would recommend using a refridgerated air conditioning unit and air cooled lights or simply waiting until summer is over.
Now you are probably wondering what to do with these two, usually different figures:
If we work on the principal that you cannot, within reason, have too much air flowing through a room and that excessive heat will damage plants, it should become a little clearer. The light calculation will usually be higher than the room calculation meaning that the fans should ideally be rated to expel heat from the room. If the room calculation is much higher, we would recommend using more light in that space or building a room within it to house the grow and save on ventilation costs. Either way, the higher rating should be used to select your exhaust fan from the list below.
Remember, you will need to bring the same amount of air into the room as you are taking out. This can be done passively in smaller rooms through air vents, though special care must be taken to prevent light leaks. It is best to use a fan for intake as it can draw the air through a smaller hole, is easier to light-proof, puts less stress on your exhaust fan making it last longer and is more accurately rated. Select a fan one size smaller than your extract fan. This is to maintain negative pressure which helps keep odours inside the room. Odours can then be eliminated by attaching a carbon filter to the exhaust or by using an ozone generator.
A cooler growing room is always a good thing as it is far harder to reduce temperatures than raise them with a heater, so don't pack too many lights in. A 600w lamp will light an area of approximately 1 m2. We recommend using 600w lamps as they give the best light to heat ratio and therefore save energy and money.
It is also a good idea to move the air about inside the room with an everyday oscillating fan. This will prevent hot spots and uneven distribution of air. Young plants that grow swaying in a gentle breeze (NOT flapping in a hurricane!) will have stronger stems too.
N.B. The light calculator will not give accurate results for air cooled lights or non-standard fans (e.g L rated, accoustic or Lineo fans). We recommend you contact us for help when calculating fan ratings in these cases. We pride ourselves on being ventilation experts and are certain we can help you with any ventilation queries.
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