Adding a second in-line fan for 600w HPS x2

[Julius Caesar]

I just added a second 600w HPS to my grow room with a dedicated intake and exhaust for the cool tubes. I currently have one 240 cfm in-line duct booster fan extracting air from the exhaust side of the cool tubes. However, with a few bends in the flex duct the single fan is not pulling enough air. I purchased another identical fan to help cool things down. I need help deciding the best place to add the second fan. I planned on adding it to the intake side of the cool tubes (blowing inward) with the existing fan extracting air out of the second HPS.


Or would I get better airflow by physically stacking the two fans together?

 

[Red1966]

The first choice seems how most are doing it. 245cfm is kind of low for a 6" fan. Mine are 345cfm. Are you using the kind that are inside a 6" duct like the attached photo? These are crap and can't overcome any back pressure.

 

[Julius Caesar]

Yeah I have two fans just like the photo you posted. I was trying to avoid the large, heavy inline fans because I wanted to mount them directly to my lights. I have a 400 cfm Hydrofarm in-line fan mounted to my ceiling for my main grow room ventilation, which should be more than sufficient for my 4x7x7 grow room once the heat from the lights is eliminated. The cool tube venting is isolated from the grow room air, but the flex duct is non-insulated so it is radiating some heat into the grow space. If the second fan doesn't do the trick I might have to insulate the exhaust side of the flex duct with a sleeve.

I am going to try and mount the second fan at the very end of the duct run. I will have to get ingenious with my mounting, but I think this will maximize the airflow. The original 240 cfm fan will remain on the exhaust side of the cool tubes. However, if I can't mount it to the wall, I might be forced to go with option #1.

 

[auswolf]

Yeah I have two fans just like the photo you posted. I was trying to avoid the large, heavy inline fans because I wanted to mount them directly to my lights. I have a 400 cfm Hydrofarm in-line fan mounted to my ceiling for my main grow room ventilation, which should be more than sufficient for my 4x7x7 grow room once the heat from the lights is eliminated. The cool tube venting is isolated from the grow room air, but the flex duct is non-insulated so it is radiating some heat into the grow space. If the second fan doesn't do the trick I might have to insulate the exhaust side of the flex duct with a sleeve.

I am going to try and mount the second fan at the very end of the duct run. I will have to get ingenious with my mounting, but I think this will maximize the airflow. The original 240 cfm fan will remain on the exhaust side of the cool tubes. However, if I can't mount it to the wall, I might be forced to go with option #1.

If you use those fans on the exhaust side of your cool tubes they won't be able to handle the heat and will fail.

 

[Julius Caesar]

If you use those fans on the exhaust side of your cool tubes they won't be able to handle the heat and will fail.

I cannot agree. From what I have read and observed myself, those fans pull air much more efficiently than pushing air.

I think I am going to try and attack the second fan at the very end of the flex duct run exiting the room. I will have to get ingenious with my mounting. Here is what my flower room looks like now.

 

[auswolf]

I cannot agree. From what I have read and observed myself, those fans pull air much more efficiently than pushing air.

Yeah it's true they do pull a hell of a lot better. But they won't last, well they might but I doubt it. I included a pic of ones I have used.(yours may be a better brand)

I used them on the exhaust of 2 400w cool tubes they lasted about a couple of months before the bearings start to seize. If they cycle with the hoods they will end up getting hard to start.

 

[Julius Caesar]

Mine has been going strong for almost 2 years so far. It cycles with the lights.

 

[auswolf]

Mine has been going strong for almost 2 years so far. It cycles with the lights.

Nice. Mind sharing the brand name or store you purchased from?

 

[Red1966]

My advise is to just use one 6" inline centrifugal fan and mount it to the wall or something. Those booster fans don't create enough pressure/suction to push/suck through that much flex duct. I used only one with two hoods and it was enough, and I had more ducting than you. If your ducting is getting more than just warm to the touch, it doesn't have enough air flow.

 

[Julius Caesar]

Nice. Mind sharing the brand name or store you purchased from?

iPower 240 cfm - $25 on Amazon

My advise is to just use one 6" inline centrifugal fan and mount it to the wall or something. Those booster fans don't create enough pressure/suction to push/suck through that much flex duct.

If these two don't cut it I will have to upgrade again. I plan on shortening the flex a bit and adding a few solid 90 degree elbows to help block light rather than s-bend the flex.

 

[RockyMtnMan]

I tried it also.
This means using 2 fans in series. In theory, for two similar fans,the cfm remains unchanged, but static pressure is doubled. If you use two fans next to each other, then they are in parallel. The cfm is doubled, but static pressure remains the same. You can do this with a Y-splitter.
There are charts for this and better explanations.
IT WON'T INCREASE YOUR AIRFLOW TO CONNECT IN SERIES.