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Cannabis Fact Contributed by: Smokey D Dope
How do I add ventilation to my grow area?
There are a couple of considerations to observe when
planning your ventilation, theyre pretty simple concepts;
but they are often overlooked.
First, remember that warmer air will naturally rise to
the top of any container, and that cooler air will
naturally settle towards the bottom.
Also remember that when ventilating any space, the
volume (VOLUME, in cubic feet or cubic meters... [L x W x
H]) of air that goes IN, also has to come OUT.
You cant expect to ventilate a grow space by simply
forcing air in, and not providing an exhaust vent.
Since the object is to remove as much warm air as
possible, and replace it with cooler air, it will be most
efficient to place the exhaust as close to the top of the
space as possible, and place the intake as close to the
bottom as possible.
Should I place the fan in the exhaust, intake or
both?
The fan should be placed in the exhaust, and the intake
should be a simple hole (or light trap, if light getting
out is a concern).
This type of system is known as an Active Exhaust,
Passive Intake System.
Mounting the fan in the exhaust, sucking air out of the
room accomplishes a couple of things...
Since the exhaust is at the top of the area, the fan
will suck the hottest air out of the area first.
The fan is actually lowering the air pressure inside
the area. Any incidental pinholes or leaky seams will
simply draw air in. If the fan were blowing IN, those
pinholes and leaks would allow potentially smelly air
OUT.
How big should the passive intake be?
It should be slightly larger than the exhaust. Remember,
the volume of air being blown out, will be replaced
through the intake. Using a bigger intake hole allows the
incoming air to be at a lower velocity (speed), which
minimizes mixing up of the air in the area. It will also
allow the fan to operate more efficiently.
How big should the fan be?
Fans are rated in either cubic feet (CFM) or cubic meters
per minute in North America. In Eurpose, metric fans are
rated in m3/hr - cubic metres per hour (m3/hr).
That means a 70CFM fan will move 70 cubic feet of air in
one minute.
Your fan should be big enough to move the volume of your
area 2 to 3 times every minute. A 70 CFM fan would be
adequate for a 35 cubic foot area, and would be optimal
for roughly a 23 cubic foot area.
To figure your areas cubic volume, multiply (in feet)
the length by the width by the height.
What if I have more than one fan? Should I use one to
blow air in and one to suck air out?
Not if the object is to provide as much ventilation and
cooling as possible.
If you have two 3-inch diameter fans, and you mount one
in the intake, and one in the exhaust, you have a total
intake area of one 3-inch hole and a total exhaust area
of one 3-inch hole.
If you use both fans as exhausts, you have TWO 3-inch
exhausts and two 3-inch intakes (actually, two 3.3 inch
intakes. They should be bigger than the exhausts,
remember?).
Twice as many holes, twice as much airflow.
Enhanced Blower Mods
Timer Options
If you find that the "Lights off" temps are lower than
you'd prefer, you can simply run the fan from the same
timer as the light by using a multi outlet power strip
connected to the timer. Plug the lights and the fan into
the power strip, and the fan will turn on/off with the
lights. If you're using more than one fan, you could
connect some or all of them, remembering that the more
fans you have running, the lower the temps will be.
* SAFETY NOTE: The timer must be able to handle
the additional electrical load, or an additional timer
must be used. SAFTEY FIRST.
Sound Suppression
Making the ventilation system quieter can be an elevated
consideration, and it's elevated to remember that the
air moving through the intakes and exhausts make noise,
as well as the fan itself. Some of the fan noise from
vibration can be overcome by mounting the fan in a
non-rigid manner. The fans can me mounted using rubber
grommets to help dampen the vibration. Self-adhesive foam
rubber window insulation can also be used. In some
installations, it can be mounted by threading a bungee
cord through each mounting hole, then attaching the other
ends of the bungee cord to the exhaust hole.
Relatively, air moving through ductwork or tubing can
become noisy, particularly if the air has to move at a
higher velocity. More, larger diameter intakes and vent
tubes will Relatively be quieter than fewer, smaller
diameter intakes and vents. The fans also don't have to
work quite as hard.
Finally, although popular and easy to use, flexible
"Accordion" type hose, commonly used to connect clothes
dryers to external vents are not always the best choice,
as they cause a great deal of drag, (making the fans work
harder) and Relatively air flowing through them is noisier
than smoother ductwork.
Filtering\Odor Control
Connecting a Carbon scrubber is a good methodology of
controlling the odor that can be a dead giveaway to an
otherwise stealthy installation. A carbon scrubber is
simply an expansion chamber (box) into which the smelly
air from a flower chamber is pumped. The chamber has a
large exhaust vent, which is covered by an activated
carbon air filter. The chamber must be big enough to
provide a damping effect of the incoming air. If too
small a scrubber is used, the fan will not be capable of
pushing air through the filter. Here, you actually want
the exhaust vent to be considerably bigger than the
intake.
There are also several DIY Odor killers available,
which work to varying degrees to provide an "Odor
Cover-up."
Remember, the term "Low Odor Strain" is relative.
Even the low odor strains Relatively still stink pretty
badly near the end of flowering.
Now go grow something!
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