Help needed, which fan

[woodydude]

Hi
I am moving my grow room around.
At present, I have 2 fans. A 5" 280m3/h(165cfm) and a 6" 715m3/h(420cfm).
Eventually, I will be using the small 5" fan as an intake fan, for now though, I will have to have a passive intake.
I have 2 cool tubes housing 600w lights.
I have a carbon filter.
The room size will be 4' x 8' x 8'

My plan is to draw air for the lights from the crawl space under the room and exhause out through the crawl space above the room and into the attic via a 10" duct I have.
The other fan will be drawing air from the room, through the carbon filter and exhausting into the same 10 duct as above.

My problem is which fan to use for the lights and which to use for the room.
I am not certain the 5" fan will be powerful enough to cool the lights.
At present, the 5" is used as an intake fan, the 6" is connected to both lights and carbon filter so is using the room air to cool the lights.

I am scratching my head trying to work out which to use for which.
Does anyone know of a calculation that may help. I only want to do the job once! Lol

Thanks
W

 

[SensiStarFan]

Hi
I am moving my grow room around.
At present, I have 2 fans. A 5" 280m3/h(165cfm) and a 6" 715m3/h(420cfm).
Eventually, I will be using the small 5" fan as an intake fan, for now though, I will have to have a passive intake.
I have 2 cool tubes housing 600w lights.
I have a carbon filter.
The room size will be 4' x 8' x 8'

My plan is to draw air for the lights from the crawl space under the room and exhause out through the crawl space above the room and into the attic via a 10" duct I have.
The other fan will be drawing air from the room, through the carbon filter and exhausting into the same 10 duct as above.

My problem is which fan to use for the lights and which to use for the room.
I am not certain the 5" fan will be powerful enough to cool the lights.
At present, the 5" is used as an intake fan, the 6" is connected to both lights and carbon filter so is using the room air to cool the lights.

I am scratching my head trying to work out which to use for which.
Does anyone know of a calculation that may help. I only want to do the job once! Lol

Thanks
W

I run two 600watt HPS cooltubes on one line and use a 4" inline fan and a carbon filter. This is the only fan I use for exhaust purposes. Air intake is passive. I have no problems with temps. Without the carbon filter hooked up (only needed last few weeks of flower) I can put my hand on the back of the cooltube. With the carbon filter on it is a little warmer but the plants below do not burn unless they stretch to within 6 inches or so of the light. Your room is 256 cubic feet and your 6" inline fan would vent your grow area more than once a minute. The 5" fan will be fine for cooling the lights. I cool my two with the 4" fan and the air being pulled through the lights is from inside the grow area.

-SSF-

 

[woodydude]

Thanks SSF
I did some calculations after I posted that last night. I thoiught they may help others so here they are.

Cool tube is 6" dia and the ducting for the cooltubes start to finish are 10' long so heres the maths.
Volume of tubes = .25" x .25" x 3.14 x 10 =1.96cf
The 5" is 165cfm so 165/1.96=84 air exchanges per minute.
In other words, the 5" fan will exchange the air inside the cooltube ducting every .7 seconds.
SSF did the maths for the room itself so here goes for the rebuild, 6" with carbon filter for the room, 5" fan cooling the cooltubes.
Peace W

 

[woodydude]

Bit of an update,
I have now rebuilt my flowering room, pics will follow when some cableing arrives.
I did as SSF suggested and put the 5" fan to cool the lights, drawing fresh air from the crawl space underneath the room. The big 6" fan is venting the room itself, via the carbon filter and yippeeee, its all good.
Temp is now at 78 lights on and has been at that all day. The lights are not quite as cool as I would like, but they are 9" away from the closest plants without burning the back of my hand (much closer and uv will burn them anyway) so overall I dont think this could have gone any better.
W