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Ventilation Question

Discussion in 'General Marijuana Growing' started by JohnCee, Aug 13, 2017.

  1.  
    JohnCee

    JohnCee Active Member

    I attempted to use ms paint and draw what my current ventilation setup is looking like, because I'm pretty sure that I could have things arranged or setup more efficiently.

    diagram.png

    I have a 315 CFM fan attached to my light reflector sucking out the hot air, and up through the ventilation to meet with the other exiting air for the the final ride going outside. Now, when I don't have my 335 CFM fan turned on to exhaust the air for my light, I can feel the other exhaust air leaking back through my light, which the diagram notes this behavior. When I turn my 315 CFM fan on it's first setting, that still is not enough to counter how much air is actually going backwards to my light, which it actually takes putting my 315 CFM fan all the way up to really move the air from the light to meet with the other exhausting air going outside.

    Could this issue be solved with a $15-$20 backdraft damper from lowes or home depot, or would I have to rework my ventilation setup entirely?
     
  2.  
    newguy123

    newguy123 Active Member

    The problem in your conception is that your fan is pushing air which lets the air flow go left or right when there is no other fan being used.

    There are two ways to correct this.
    1- install a backdraft damper where you don't want the air to go through.

    2- put the fan next to where you exhaust the air so it pulls from everywhere else.
     
    Dr. Who likes this.
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    xtsho

    xtsho Member

    Are you using T ducts? You should use a Y duct. It will direct the flow out much more efficiently.

    [​IMG]

    [​IMG]
     
  4.  
    JohnCee

    JohnCee Active Member

    I'll likely have to go with the backdraft damper, simply because I am utilizing all of my fans, and I am trying to address a heat issue that I am currently having. I figure the fan would be best served actually on the light fixture to immediately remove the heat, however I could tell that the fan was struggling to keep up so I had to investigate the issue.

    I'm actually using " T " ducts, which would explain some of the issues that I am having. I don't know which route to go now, should I get the backdraft damper, or shoot for a " Y " duct to assist with airflow?

    --

    Once I have air flow going in the correct direction, it should be a lot easier for my 335 CFM fan to keep my 315w CMH light cool, correct? I am able to stick my hand under the glass of my reflector about 5-10 inches down and I'm still feeling quite a bit of heat. I figured that having the 335 CFM fan directly attached would remove that heat, however with the air flow issues that I have been having it's hard to say how much effective my fan could have been at cooling the light. I'm looking at it like two wind tunnels merging and forced down a " T " duct, but hoping a backdraft or " Y " duct would give me enough gain since winds won't be competing to effectively cool my light down.
     
  5.  
    JohnCee

    JohnCee Active Member

    I'll be heading over to the hardware store tomorrow, should I be shooting for the " Y " ducting, or the backdraft damper?
     
  6.  
    newguy123

    newguy123 Active Member

    The Y ducting will reduce pressure loss and the backdraft damper will eliminate backdraft. Two different things
     
  7.  
    Dr. Who

    Dr. Who Well-Known Member

    Only thing to add to this is - You ALWAYS PULL the air, NOT push it!
    The exhaust fan should be at the end of the area being exhausted.
    The fan can "push" the air at any point after any turns or connections, past the exhausted area.....
     
  8.  
    Lordhooha

    Lordhooha Well-Known Member

    I agree the fan should be at the end where air is running outside PULLING the air outside. The setup now is inefficient. Also depending on the size of the rooms you may need more fan. But that's just me and I like having a good negative pressure in my rooms. @JohnCee
     
    Dr. Who likes this.
  9.  
    JohnCee

    JohnCee Active Member

    I thought the pressure loss was attributed to the fact that I am having backdraft?

    I suppose the pulling air and not pushing it depends entirely which fan you are looking at in regards to the situation. The fan I have mounted onto my light fixture is most definitely pulling the air out of the light fixture, however it's then pushing the air until it runs into the other exhausting air. The fan that I have extracting air out of both grow rooms is pulling the air out of the rooms, but then pushes it to the exhaust. To my limited knowledge -- I am pulling the air instead of pushing it. In total there is about 25 feet of ducting to work through, with a 400 CFM fan pulling air from the rooms and 335 CFM fan pulling air from the light fixture.

    What you guys are saying is that I could attach the two " T " ducting together, and then put the green 400 CFM fan on the end of the " T " which is being exhausted out, labeled "GOING OUTSIDE", correct? If I am following correctly that should help with the pressure loss AND backdraft, or will I still have to do something in regards to a backdraft damper or " Y " ducting?
     
  10.  
    Lordhooha

    Lordhooha Well-Known Member

    It won't matter if you put it on the run going outside pulling the air it will pull from all the runs out
     
  11.  
    xtsho

    xtsho Member

    Your situation is different than mine. I have a 4 x 4 tent and my fan is in between a carbon filter and the light pushing air through the light. It works for my setup but yours is different. I can tell you however that using the Y ducts I got much better flow than with the T ducts. If you pull the exhaust through instead of pushing it you will eliminate the back flow issue you're having. Regardless, the Y ducts are much more efficient with regards to airflow. The reason I needed to split the airflow was because I had to move a portable air conditioner into the tent when we hit some 100 degree days. A T duct wasn't working very well and once I swapped it out with a Y duct the airflow increased significantly. It's easy to just look at the two different pieces of ducting and see why the flow is better.
     
    newguy123 likes this.

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