intake/exhaust question
- Thread starter tpemiles
- Start date
NLXSK1
Well-Known Member
Your airflow depends upon the size room/cabinet you are ventilating.
Typically you want to create a slight negative pressure inside the grow room by having the exhaust air be more than the fresh air.
This will cause fresh air to be drawn into the grow room and can help with the smells of the grow.
Without having any size references it would be hard to help you out more.
Typically you want to create a slight negative pressure inside the grow room by having the exhaust air be more than the fresh air.
This will cause fresh air to be drawn into the grow room and can help with the smells of the grow.
Without having any size references it would be hard to help you out more.
NLXSK1
Well-Known Member
That is a big light for a small space. You may want to consider a vent in the HPS hood with it's own fan.
The reason that you want negative pressure in your tent is that if you have positive pressure it means that the air is trying to find ways to escape the tent.
That means it will leak out of cracks, gaps, zippers, etc.. So, no matter what you will still smell something. With negative pressure you have air trying to get into the grow room in all these small places so the smell only goes to the exhaust and is easier to control.
You dont need alot of negative pressure, just a very slight one to do the job so I would always put the bigger airflow on the exhaust side of the ventilation. Also, a rotating fan should be used inside the cabinet if at all possible to mix the air.
The reason that you want negative pressure in your tent is that if you have positive pressure it means that the air is trying to find ways to escape the tent.
That means it will leak out of cracks, gaps, zippers, etc.. So, no matter what you will still smell something. With negative pressure you have air trying to get into the grow room in all these small places so the smell only goes to the exhaust and is easier to control.
You dont need alot of negative pressure, just a very slight one to do the job so I would always put the bigger airflow on the exhaust side of the ventilation. Also, a rotating fan should be used inside the cabinet if at all possible to mix the air.
yancey
Well-Known Member
hey, i understand about how the negative pressure would keep the smell from leakn out, but i also thought it was the other way around, so you would have the air circulate more? dunno anything about this jus wonderin myselfi was thinking about a 3x3x6 box with a 400w hps. will that be enough? and you want more exhaust than intake to get fresh air? i thought it was the other way around. good think i talked to you first
NLXSK1
Well-Known Member
It really is not about air circulation, it is about air pressure.
Drive a car down the road really fast with only the drivers side window down. The air in the car will be overpressure dut to a large volume of air being driven into the car.
However, circulation is for shit because you have not given the air anywhere to go.
Now, open the passenger window and we really have ventilation happening. The car is still overpressured but because we have provided an escape we now have easy airflow.
Negative airflow is harder to demonstrate but if you go to a very large building such as a shopping center and open the door the air will either rush in or out. If the air rushes in it means the building is under negative pressure and that the outflows (ventilation) is exceeding the inputs.
That is also a demonstration of scale... You can have positive and/or negative pressure in something smaller than a soda bottle or larger than an enclosed stadium.
Anyway, there is no easy way to measure your actual airflow due to impedence of ductwork, different equipment, etc...
The point is to try to generally have more air exhaust that you have coming in. If you have a 4" inline duct a 6" exhaust duct with a fan would be nice... If you have a 8" inline duct maybe a 10" exhaust duct would be good, etc...
Otherwise depending on how tight your setup is the air will leak out from every little crack and that could allow the smell to escape too. It also shows like the car with only one window open how not allowing for exhaust can mess up both sides of the ventilation system.
Hope that helps.
Drive a car down the road really fast with only the drivers side window down. The air in the car will be overpressure dut to a large volume of air being driven into the car.
However, circulation is for shit because you have not given the air anywhere to go.
Now, open the passenger window and we really have ventilation happening. The car is still overpressured but because we have provided an escape we now have easy airflow.
Negative airflow is harder to demonstrate but if you go to a very large building such as a shopping center and open the door the air will either rush in or out. If the air rushes in it means the building is under negative pressure and that the outflows (ventilation) is exceeding the inputs.
That is also a demonstration of scale... You can have positive and/or negative pressure in something smaller than a soda bottle or larger than an enclosed stadium.
Anyway, there is no easy way to measure your actual airflow due to impedence of ductwork, different equipment, etc...
The point is to try to generally have more air exhaust that you have coming in. If you have a 4" inline duct a 6" exhaust duct with a fan would be nice... If you have a 8" inline duct maybe a 10" exhaust duct would be good, etc...
Otherwise depending on how tight your setup is the air will leak out from every little crack and that could allow the smell to escape too. It also shows like the car with only one window open how not allowing for exhaust can mess up both sides of the ventilation system.
Hope that helps.
NLXSK1
Well-Known Member
Thinking about these things is part of my job. Your welcome, happy to help!!