As a matter of fact air is quit simple because there's only one thing to go wrong:
Not Enough Of It.
Commercial greenhouses have the ability to change the complete volume of air in about two minute's time. Maybe this is a bit overdone for our purposes, but it shows us the significance of air for plants.
As I already told you, the carbon dioxide in air is needed for the plant's photosynthesis process. In a closed environment, plants could use up all of the CO2 in less than half an hour, especially when it's hot.
In exchange oxygen, water vapor and odors are released to the air, which we want out of the room ASAP.
The process of building sugars under the influence of light and CO2 is called assimilation.
At night, from these sugars new cells are formed, a process we call dissimilation. For the latter process oxygen is used. Also roots need oxygen as a source of energy, to much CO2 at root-level could even be poisonous. But generally speaking plants produce a lot more oxygen then they use themselves.
In modern greenhouses CO2 is sometimes added as extra nourishment. Especially with higher temperature's bigger harvests are possible.
A word of advice: although CO2 can result in better yields I wouldn't use it inside my house. The gas itself is not poisonous, but it is dangerous because it is heavier than air, and it will not just mix: it tends to replace the air.
It also replaces the oxygen in our blood, so you would simply suffocate.
In other words, if anything should go wrong, you, your children, visitors, or your neighbors might never wake up.
Getting enough air in and out of the growing-room is one of the biggest problems.
Although Haze doesn't smell as bad as Skunk (well, that's my opinion ;-), there still is a considerable amount of smell to get rid off. Besides that the plant needs a lot of fresh air (I know; I am repeating myself).
If you only have one lamp in an enormous room there is not much of a problem. Difficulties start when your room is smaller or when you have more lamps. In this case you really need the help of strong ventilators plus some sort of passage to get air in and out.
Chimneys are near perfect, well if not in use that is.
Sometimes you don't even have to worry about smell since chimneys are designed to get their exhaust into the higher winds.
Apart from that there's always a bit of natural draft so even when ventilators are out you'd have some ventilation. This could be an advantage at nights.
During daytime (When the lights are burning, remember?), this natural ventilation will hardly be sufficient so you'll have to help nature's forces a bit by means of a mechanical fan.
If you don't have a chimney or another kind of funnel, you'll have to fabricate something yourself.
As a last result you could simply run a hole through the wall. Aside from attracting attention, strong winds might stop your ventilation from working properly. There's also the problem of not knowing where the smell will go.
A way to avoid problems with smell is to make use of an activated carbon filter. This would take care of 99% of the smell. Filters however cause extra resistance, as do flexible hoses and curved funnels. This is something you have to take into account when buying a fan.
IMHO one fan should be enough for your ventilation-system to work.
Use it to get the air out, if possible from the top of the room. By making a hole on the opposite site of the room air will be sucked in due to the underpressure caused by the fan. Of course you could make more then one hole to get air in. As a rule of thumb make the surface of the hole(s) were the air enters three times bigger than the surface of the hole you use to get air out.
In contrary to the problem where to leave stale air, it doesn't matter too much from where you obtain fresh air. Depending on the climate and the time of year you could get it in from your house, nicely pre-heated in winter. In a hot summer you need lots of air, so you get it in from as much places as you can think of.
An advantage of using only one fan to get air out is that air gets sucked in through all cracks and holes that might be in your room's walls. Because of this, it is humanly impossible that smells do escape by any other way than you intended (i.e. through your filter).
We still have a major problem, how to get the air in and out, without light seeping through the holes? The answer is in Greek mythology, a labyrinth.
A labyrinth is a construction that allows air to enter (or leave) freely, without allowing light to pass through.
To save a thousand words I will add a picture, albeit a very schematic one. On this picture you have a view from the side, and of course this side has to be closed too. You can make one from a cardboard box, black and white plastic, or whatever material.
If you want to do things as they should be done, make one out of triplex or any other plywood. To keep light from reflecting, use black non-shining paint like the one they use for chalkboards, and paint the whole thing black. Make it as big as possible to reduce air flow resistance.
It's not easy to say what fan is the best for our goal.
One thing's for sure though, apart from the lamps, it's the most important piece of equipment you have to buy so don't try to save money here.
Off course you are restricted to the measure of the funnel used as an exhaust. You simply cannot push 2,000 cubic meters of air through a 125 mm tube. Also long ducts with curves, filters, etc., add up to more resistance, which you have to take into account.
In accordance with all of the above you can calculate the maximum capacity of the fan you need. Or you could have someone with experience in air-conditioning calculate it for you. Buy the maximum-capacity fan you could use, not a lighter one!
Remember that you can always use a dimmer to reduce the airflow of a heavy fan, but you cannot make a fan run any faster if its capacity is insufficient.
Probably the best buy for your money is a squirrel cage ventilator. They are relatively cheap to buy and also have the best relation between electrical power-consumption and airflow.
Watch out for bargains when buying a fan.
Cheap fans could produce a lot of vibration because of bad construction and these vibrations carry a long way through walls et cetera.
It's possible that you don't hear a thing, but a few blocks away people can tell exactly when things start up with you, because of the resonance of the exhaust-fan.
A remedy for this problem is to mount the fan to the wall with rubber blocks (go to a Harley-Davidson dealer and ask for the blocks to mount an oil-tank).
Another way is to hang it from the ceiling using rubber straps.
By using a small piece of flexible hose to attach your fan to the exhaust-funnel you prevent vibes passing through here.
Another source of noise could be the hissing sound of the air being blown out. Try to make the inside of funnels as smooth as possible to keep turbulence to a minimum.
Besides a fan to get air in and out, you need a few normal fans to keep the air in motion.
The oscillating tabletop-fans you can buy at any hardware-store are ideal for this purpose. For the reason of why we have to move air around we need some more theory.
Water and nutrition is picked up by the roots and transported throughout the plant. The mechanism behind this transport is rather complex and still not fully understood.
It's a combination of roots giving pressure, osmosis from the cells and the transpiration through the (stomata of the) leaves.
Plants do not have an active breathing-system as we humans or animals have. If the air around the leaves stands still, humidity will rise and affect evaporation, thus decreasing the total sap-flow.
Also the plant will use up CO2 in unmoving air in no time, so you have to make sure it is refreshed continuously.
Furthermore, by moving the air around you won't get local differences in temperature and humidity, and insects and molds are having a harder time. Last but not least, plants get stronger from the motion induced by the flow of air.
Because Haze plants tend to get big, it's always a good idea to ventilate below the canopy of leaves as well.
A very nice way to equalize temperature is vertical ventilation.
During the summer, one could pump the relatively cool air from the floor to the ceiling by means of a fan and hose. During the winter, turn the fan around so you pump the warmer air down.
If you use vertical ventilation you need to vacuum-clean your room a bit more, because of dust being blown around. But having a clean room also helps avoiding pests, like bugs and molds so you have to clean regularly anyhow.
Remember that gardens with the most fans most of the times have the best results, especially if they are in use.
In case you're using non-oscillating fans to move air around internally, don't directly point them to your plants. This will cause windburn on the leaves.
Fans need to be started "full speed", after this you could turn them down a bit. Oscillating fans also have to be moved around, which makes things harder for the (small) engine.
Never, ever use a time clock to switch a ventilator unless it is set full speed, it could be that it "hangs" and won't start up at all, which could cause a fire.