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Why is ventilation so important?
(Contributed By Sureshot)

Ventilation is almost as important as lighting. Plants have the rare ability to manufacture their own food, this process is called photosynthesis. The main substance in this production, chlorophyll, uses light energy to convert carbon dioxide from the air and water and nutrients from the ground into food sugar. When these elements abound in a perfect environment, the production of food is limited only by factors that effect photosynthesis, in this case the AMOUNT OF CARBON DIOXIDE RECEIVED.

A good ventilation system will allow your plants to always have a fresh supply of CO2 whilst removing the waste gases that are unproductive to the plant. Ventilation is also an important factor in keeping the temperature of your grow room within an efficient growing range.

A further factor that makes ventilation so important is humidity. High humidity can lead to bud rot in high density strains and good air movement within the room will reduce this.

How do I measure temperature correctly?

In order to correctly gauge the temperature of your grow space you must first have an understanding of the heat produced within your grow space. There are two pertinent temperatures in your grow space, the air temperature and the radiant temperature.

Air Temperature

Air temperature is fairly self explanatory, it is the measurement of the heat content of the air or to be more scientific "the ambient temperature indicated by a thermometer exposed to the air but sheltered from direct solar radiation".

Air temperature is measured by a standard mercury bulb thermometer and is generally the temperature people are talking about when they talk about keeping your grow space at a regular 75 to 80 degrees.

You must be careful when measuring air temperature to avoid the measurement being falsified by the presence of radiant heat. To do this make sure your thermometer is placed out of direct light where the bulb cannot be heated by the warming radiant energy.

It is best to place your thermometer on the wall of your grow room at about about the level plants are growing at, exposed to the same air as the plants themselves. Be sure to cover the bulb with something to keep out radiant energy.

Radiant Temperature

Radiant temperature in the case of growing is the heat that is mentioned above as "direct solar radiation". In a general sense however radiant heat is the result of the fact that all objects lose heat through radiation to objects of a lower temperature. The sun's radiation is a good example. A person immediately senses the radiation when walking out of the cool shade and into the sunlight.

Simply speaking, because the lamp is hotter than the plants foliage, heat will transfer from the lamp to the foliage, this transfer is essentially independent of air temperature. This is why thermometers should be covered when measuring temperature.

Plants can take a much higher radiant temperature than air temperature and this can be gauged using the simply hand test. Place you hand slightly above the tops of your plants and if after a few minutes the heat from the lamp becomes uncomfortable, then it probably is for your plants too.

This is only a very loose rule of thumb but given our favorite plants variety of natural growth environments I'd say it would do for 99.9% of growers out there.

What should I consider when planning the ventilation for may space?

1. The size of your space. Multiple the length x the height x the depth to get the Cubic space of your grow space. This can be done in feet or metres but most work in feet.
2. Whether your ventilation is needed to cool the space or simply to replace depleted CO2 levels.
3. Hot air naturally rises and cool air naturally sinks.
4. Air needs to both be exhausted and intake, air in, air out.
5. Moving air creates noise, both the fan noise and the air moving.

What is CFM and how does it help me work out how much ventilation I need?

CFM stands for Cubic Feet per Minute and is the amount of air a fan will shift in that time. Every good fan will have a rating of this kind. Let's say you have a fan with a rating of 200 CFM; this fan will exchange the air in a 200 Cubic Foot room once per minute or the air in a 100 Cubic Foot room once every 30 seconds.

In order to lower temperatures in a room with a large HID you will need to exchange the air in your space about 3 times every minute. Multiple the length x the height x the depth to get the Cubic space of your grow space.

Example Grow room spec:

4 foot wide, 5 foot deep and 5 foot high
= 100 Cubic Foot.

To lower temperature with say a 1,000w HID you'll need to exchange air 3 times a minute so a fan with a CFM rating of around 300 CFM will be required. If dealing with above average temperatures it may be worth exchange air up to 5 times a minute.

How much ventilation do I need?

Simply work out the Cubic Footage of your grow space and multiply this by the number of time per minute you wish to exchange the air in the space (3 recommended) to get the CFM rating of the appropriate ventilation.

Work out the cubic space of the space and buy fans with the appropriate cfm ratings in order to get the right amount of air moving in and out of the grow space.

A catch all formula I saw once for working out the amount of cfm you need is which doesn't take into account the space size but does consider the different heat levels of different wattage lamps is:

(3.2 x watts) / (Grow Room Temperature F - Cool Intake Air Temperature F) = CFM

So, if you have 1,000 watts, want 80 degrees in your grow space and the ambient air temperature is 70 then:

(3.2 x 1,000) / (80 - 70) = 320 cfm

Considering this alongside the example in the question regarding CFM (above) where the room size was 100 cubic foot and a 300 cubic foot fan was required to exchange air three times a minute, you can see how the two methods can be used alongside each other to spec out your ventilation very comprehensively.

Example

Room size = 3 x 4 x 5 = 60 Cubic Foot
Lamp Wattage = 600
Required grow temp = 80
Summer ambient temp = 75
Winter ambient temp = 70

Summer Tolerance
(3.2 x 600) / (80 - 75) = 384 cfm

Winter Tolerance
(3.2 x 600) / (80 - 70) = 192 cfm

Space Consideration
60 cubic foot room, exchange air 3 times, 60 x 3 = 180 cfm.

In this example the summer tolerance may be a little high but given the choice of a 4 inch, 6 inch and 8 inch inline fan it may still be worth going for the middle of three (example mid end stats below) to give you some potential for temperature control (using a variable speed control) and/or expansion.

Example Fan Stats

Vortex 4 inch Inline Fan 172 CFM
Vortex 6 inch Inline Fan 392 CFM
Vortex 8 inch Inline Fan 747 CFM

Elicent AXC100B 4 inch Fan 152 CFM
Elicent AXC150B 6 inch Fan 309 CFM
Elicent AXC200B 8 inch Fan 636 CFM

What type of fans are available?
(Contributed by MacGuyver)

Growing plants requires ventilation, especially when running HID lighting. To get a decent result, you'll need an exhaust fan. This FAQ will discuss types of fans, how to set them up and also have a section on odor control. For your exhaust, you should have at least 150 or so CFM per 1000W of HID light

Section 1 - Types of Exhaust Fans

There are several types of fans you can use, all with pro's and cons. Here are the four main types

Bathroom Fans

Bathroom fans usually blow between 50CFM to a little over 100CFM. They work on the same principal as the squirrel cage fans (see below) but are not made to the same quality or power. They are OK for a small grow with one 400W lamp or so, but not much else. They also aren't designed to have ducting mounted on the intake, so using them with vented reflectors* or carbon filters? is out of the question. They can also be quite noisy for the amount of air they push. They're certainly not optimal, but they are cheap.

Pros: Cheap
Cons: Everything else

Air Booster Fans

Air boosters were designed to be installed in home H-VAC ducts to boost airflow to rooms that are far away from the furnace, and have poor airflow. They can push up to 200 CFM, and are fairly quiet. They were designed to operste within a duct, so using them with vented reflectors easy to do, you can also use them with smaller carbon filters. They are very inexpensive. They'll do the job for most single lamp grows.

Pros:Cheap, Installs in a Duct, relatively quiet
Cons: Not all that powerful, CFM ratings are questionable

'Squirrel Cage' Blowers

These fans have been used in , H-VAC systems for years. They are powerful fans that suck air in from one or both sides and blow it out an opening. Some disadvantages are that it can be a pain to attach inflow ducts to the side inlets, unless you enclose the whole fan in a box or ventilation 'room' so again, vented reflectors and carbon filters can be troublesome to use with squirrel cage fans. They also produce quite a bit of vibration, and are relatively loud. They do however produce the most CFM per dollar you spend, so they are very economical.

Pros: Powerful, reasonably priced
Cons: Loud, cumbersome to attach accessories.

Centrifugal In Line Duct Fans

These fans are the top of the line. Specifically designed for hydroponic applications, they are powerful, quiet, and unlike the previous fans, are speed adjustable. Carbon filters were specifically designed to work with these fans, so they'll usually fit perfectly. Ducting is also easily connected to them. The only disadvantage, which you've probably guessed by now, is that they are somewhat expensive. In my opinion however, they are well worth it, and most come with a 5 year warranty. You'll usually want to have duct on both ends of the fan to muffle the sound. Although they produce almost no vibration, 435 CFM rushing through a 6" hole will make some noise.

Pros: Quiet, Powerful, Easy to set up, speed controllable.
Cons: Somewhat Pricey

* Vented reflectors are reflectors which a duct can be attached to vent heat directly from the source
? Carbon filters are a large perforated cylinder filled with activated carbon, and usually have a pre filter as well. They are by far the most effective way of elimination odors in your exhaust.

What types of odor neutralizers are available?
(Contributed By MacGyver)

One thing about growing our favorite plant that cn be a real pain is the stink. There are several options here, from something as simple as an air freshener to things like carbon filters and electronic ozonators.

Air Fresheners

Ths is quite a large category in itself. An air freshener can be as simple as the pine tree hanging from your rear view mirror to a digital dispenser that can be custom programmed.

They all do pretty much the same thing, and that's mask the odour. Many of the auto-dispensers have things like ozium that neutralize odor. I find one of the most effective is tour simple Glade Scented Oil. It does a pretty good job for a small, or even a larger grow, and is dirt cheap and available in many scents.

Auto-dispensers can be hard to find outside of a hydro store, or ripping one off from a public toilet (which I do not encourage) Try calling Orkin Pest control, as auto dispensers for air freshener / insecticide are often distributed in bathrooms by them. Regardless of your odor control system, you should always have some air fresheners around anyways.

Pros:Cheap, pleasant smell
Cons: Generally just masks odor.

Ozone Generation



Ultraviolet and Corona Discharge Ozonators pictured respectively

Ozone is fairly effective at neutralizing odors. It works by attaching on to the odor molecule and causes them to drop to the ground or wall. O3 generators create Ozone from either an uvtra violet bulb(s) or by corona discharge, Corona discharge is basically arcing electricity, and the electricity arcing through the air splits oxygen molecules, and the free oxygen atom joins up with an O2 molecule to form 03, or ozone.

Unfortunately ozone is toxic, so IMO they should not be left on for long periods unless they are the type that fits into your exhaust vent. With the exhaust type ozonators, you should have at least 10 feet of space between the ozonator and the vent that your exhaust comes out of, this is to allow the ozone to react with the odour particles. Ozonators help with the smell quite a bit, but I find the smell is usually still pretty noticeable.

Pros: Units are Small, easy to install in ducts. Relatively effective for small grows. Low maintenance.
Cons: Expensive, not very effective for a large grow or stinky strain. Ozone is toxic.

Carbon Filters

Carbon filters are by far the most effective odor control system out there. They consist of a large, double walled cylinder, filled with activated carbon pellets around the outside. They also usually have a pre filter that extends the life of the filter by preventing dust and particulate matter from getting into it. Exhaust form a carbon filtered grow is odorless. Carbon filters need replacing every 1 - 1½ years.

Pros: The most effective option in odor control, They don't produce any other odor
Cons: Expensive, fairly large and bulky, Need replacing more often than an ozonator.

Negative Ion Generators

I've never tried them myself. They work on a similar principle as ozone - the negative ions attach to odor molecules and cause them to become non airborne. However any feedback I've heard about them concerning eliminating grow odors is that they are absolutely fucking useless. In addition to that, they are even more expensive than Carbon Filters or Ozonators. Don't bother with them.

Pros: Sleek, modern design. Conversation piece
Cons: everything else.

Can I build my own odor neutralizing device?
(Contributed By phat pharmer)

This design was taken from some posts on OG and CW, it's basically a bucket filled with gel and odor neutralizing agent with a PC fan blowing air through it.

I have used this to completely hide the smell from a couple of 2 plant grows, and recently it did pretty well with a grow of 6 Bubblegums. I even used it while drying to mask the smells from that.

What you will need is:

• Some hanging basket Gel - used to keep moisture in the baskets, it's a silica gel type stuff that can absorb a lot of water, most garden centers sell it.
• Some ONA - I bought this from a local cleaning supply company, about £8 for a liter that has done 3 grows now.
• A bucket and lid
• A PC fan

Next cut a whole in the lid to fit the fan and bolt it in place.

Drill some holes around the top of the bucket. These will allow air into or out of the bucket depending which way you power the fan. Add the gel and add water until it can't take any more, then add a cupful of the ONA and you are ready for action.

For my small growbox I connected the bucket to the outlet using some lemonade bottles so it filtered the air on the way out. In my larger growbox I just put the bucket into the growroom and let it do it's thing in there.


Editors note: It may also be worth adding this to your existing inline exhaust system, though some experimentation with the size of the intake holes (into the bucket) may be required.


Should I heat my grow room?

It may be necessary in a very cold winter to heat your grow space but this can be difficult and hazardous. Anything that blows hot air is a bad idea due to it's affects on humidity and the possibility of heavily drying foliage.

It may be advisable to raise the temperature of the ambient space rather than the space within the grow room or even add another bulb. Another possibility may be turning down your ventilation from a few times a minute to every minute of less as well as a better insulated a grow space.

CloudCity

I have a couple of grow room questions. My ambient temp is 74 degrees with 40% to 50% ambient humidity. My grow room has a very skunky smell, and I'm still in the vegetative phase of my grow and am wondering if this is normal. BTW, this isn't my first grow. I have a commercial grade ozone generator, but I'm wondering if I should even use it yet. And if I do use it now, how far from my grow room should I put it? Next, I'm wanting to use some CO2, but is it too early to do it yet? Do I wait until I start the flowering phase? I plan on buying dry ice from my local grocer to supply my grow room with additional CO2, but given the fact that it's pricey, how much and how often should I use it, Also, it's already winter here (I live at over 10K feet) so I don't want to draw undue attention to the fact that I'm using a fair amount of dry ice in the winter, We've already had snow......yesterday and today as well as last week too. I'm using a big humidifier to boost the humidity level, but still having trouble and was wondering what the ambient humidity should be. Thank you very much for your time and the effort you put into your post. Very helpful and greatly appreciated.
Peace brother!
CloudCity

p1293

First post btw. Hopefully it is a good enough question to receive an answer. I am "considering" starting my own project and I believe I have got most of the angles covered except for that one called smell. I guess you could say I live in a neighborhood. I am only contemplating three or four plants. First grow so I am not too sure how bad the smell is. I am wondering if it is going to be bad enough to smell it outside my house? Another note I was laying in bed doing my best thinking which is where it normally happens and I had an idea. Done a little research on it but really only found like one article about it on the WHOLE internet. So im not too sure how effective it would be. Anyways enough with the suspension. I am considering air filtration using a water method. Simply meaning running my exhaust/odor extraction vents leading from my room into a considerably large tub containing water. Do you think it is possible if I have a constant flow of air causing it to be pumped into the water causing bubbles. Do you think the smell could be filtered that way. Im sure the system would have to be precise as far as pressure and what not, but does it sound possible. Any inputs appreciated.