Spring 07
Its the beginning of April 07.  The start of Spring as well as the beginning of a new outdoor cannabis growing season.

Round about now, urban guerilla's in the UK will be thinking about whats going to be planted, and where.

There's lots of planning to be done if your plants are going to survive a possible 6 months outdoors, fending for themselves.  So any time invested now will pay back later.

 

  short duct runs maximise efficiency..

 

Indoors
Meanwhile, indoor growers are about to have a whole new set of issues to deal with as the temperatures start to rise as the weather gets better.

You can set your watch by it.

Every year, and at exactly the same time, the online message boards start receiving questions about increasing temperatures in the grow room.

In April 2006 growers were already reporting grow room temperatures of 35c, and switching off lamps as a result of it.  I wonder how many made the necessary modifications to deal with this next Spring warm up which is happening as I speak?

 

Hydro shops?
It has to boil down to how people research their project before brandishing their flexible friend?

Its too easy to walk into a grow shop..any grow shop, with a credit card in hand, and ask to be "kitted out".  But be warned..you're about to be fleeced, and whilst your being fleeced, there is a chance, (a good chance) that the equipment you bought wont do the job you want it to do!

 

Here's the science.
Your ventilation system does a lot more than simply remove heat from the grow space.

Put simply, you can have as much of the very best branded 'everything else', but if your ventilation isn't up to scratch, you will experience problems with not a hint of an "if" or a "maybe" about it.  Period!

In the grow shop
Picture the scene.  You're in the grow shop and you say to the person behind the counter, "I need a fan".

"How large is your space", asks the grow shop owner.

You tell him how big your grow space is, and he recommends a fan to you!  Sound about right?

 

Here's the problem
The majority of industrial ventilation fans we use today are designed specifically for a task in hand.  That is, to ventilate and exhaust a network of smooth ducting which has long straight runs of smooth aluminium 'box-section' ductwork.

Given a set of industry standard criteria to meet, each industrial fan has a tangible set of operational parameters (and limitations), depending on the size of the fan.

So we tell the grow shop owner the size of the grow space, (in this instance a converted wardrobe or similar), and we're recommended a four inch "closet extractor" inline fan, which will "passively vent" a converted wardrobe with "no problem".

The S&P closet extractor is a good little fan.  A great fan even, and I'm using it as its simply, one of the best known examples.

It comes with the unique feature of being able to remove the fan motor assembly for cleaning, without having to remove the ducting!  Thats a great feature for someone who is putting together a compact, stealthy grow unit.

The problem is, with so much equipment to install in such a confined space, room to install a fan, carbon filter, associated ducting, light & reflector etc, is at a premium so corners need to be cut.

What invariably happens is the fan gets shoved into either a top corner, or outside the grow space altogether, and its all linked together with metres of kinky ducting, (calm down dear, I mean bendy).

And get this!  Every 90 degree turn in your ducting see's a loss of efficiency equal to 50% of that whats available.

 

How many bends you got in yours?

With 2 or 3 bends, the fan might as well not be there, and you're wondering why your grow room is hot even though you only recently installed your new fan, and its not yet summer?

 

Dont 'buy it now'!
A 4 inch fan is only going to passively vent a grow room if a couple of important rules are followed.  This applies whether you grow in a grow tent, or something a little more solid and permanent.

Growtent?
If your planning on growing in a grow tent, the environmental factors are a little different - somewhat more 'flexible'.

The problem lay in the 'soft' construction of the walls.

When using a single fan and passively venting a grow tent, the sides f the tent are actually 'sucked in' toward the middle of the tent.

How airtight the tent is, will determine how obviously this shows up, but in some instances it can be quite dramatic.  Almost as dramatic as the loss of ventilating efficiency your grow room is experiencing.

Essentially, the outer skin of the tent is acting as 'super thick air', which the fan is trying to pull through the ducting.  Obviously this has an effect on the overall efficiency of your ventilation system and if you're experiencing heat issues in a passively vented tent, this will be playing a part as the fan pulls its guts out against the flexible construction of the tent.

 

..the hard stuff
In a grow space constructed solidly from timber and plyboard, the fan isn't trying to 'implode' the grow space.  Well it is, but not with such a dramatic visual display of science.

Its having to move only air, with far greater efficiency the nett overall gain.

So to get some sort of syncronicity when ventilating a grow tent I would recommend 2 fans, to combat this loss of efficiency as installing a larger fan, just serves to make the inneficiency problem worse!

Passive
So passive venting is not really suitable for small growers?

Thats not the case at all.  Set up correctly, passive venting is a good way of getting loads of fresh air laden with CO2 into your plants.  But the key is in how its set up!