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fan sizes intake v out take

Hello again, ive a question for the knowledgable. 

I am having difficulty controlling my temperatures in my room.

I have a 8 inch A1 intake fan 750 m/hr

and 2 out takes both 12 inch 1300m/hr.

I have 4  x 600w lights in the room.


One of the out takes is run off a variac and is dialled in at 40%, as its quite loud outside. This is run constant at 40%, doesn't change.

the other intake and outtake is worked off the other twin variac fan controller  so 8 in 12 out.  At about 50% the temp remains stable at 27, with 400W lights.


I was having heat issues with my lights at 600 so have had to turn them down to 400w. 

when I ran the 600s, the temps were around 32, when I ran the 400s the temps were around 29

I also had a silencer inside the room attached to the intake fan, which must have restricted it in some way, because when I took it off the temps in the room dropped 2 degrees, to 27, with the 400s - amazing eh? I tried again with the 600s but couldn't get them under 31 degrees.


Now I was thinking about getting some air cooled hoods to keep temps down and allow me to run the 600s, BUT, im now wondering if I upped my intake fan size, if this would work? and be a better alternative (obviously it would be better than air cooled hoods, but would it be enough to drop the temps down, say 6 degrees. im very doubtfull myself.)


I was thinking of using the noisy 12 inch extract as an intake, and using the 8 inch intake as an out take, as I would be able to up the rate of exhaust, as it wouldn't be so noisy?


what do you think?  bigger intake or air cooled hoods?

The only  advantage of air cooled hoods is that I could squeeze another light in there, so I would have 2 HPS and a MH, above the scrog for a better light spectrum..


Opinions,? what would you do?

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I might be wrong m8 could be high temp outside the groom which is being brought through the 8inch intake although I'm sure sum1 will be along soon to help 

Full of good helpful people on this forum in my experience..... 

Also just to add a pal of mine extracts with a single12 inch and a 8 for intake with 4 600s and is able to keep temp at optimum so again I may be wrong but try a single 12 rather than 2 if you catch my drift 

All the best pal




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My advice is leave it be. We've just about finished with the hot weather


I bet 99% of us have struggled with temps in summer. Its how it is but they dont die



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The hot weather up here was finished before I set this up.

its only been between 13 and 16 degrees outside since I set this up and turned it on 5 days ago,so its hardly roasting

.its more like a normal average temp I would have said..


I know they wont die, but the higher temps in the room is affecting the water temps in my DWC buckets, and not in a good way as they are up to 24 degrees, which isn't good, and that's with them being insulated, so im gonna have to do something.

Im running more air through them in the meantime, but that's just putting off the inevitable isn't it?


Any thoughts on the fan sizes or hoods?

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I think I'm familiar with the temperatures you experience although maybe not as cold as up north as you. I'd bring in more air and leave air cooled hoods as last resort. Temps will be plummeting now we in to September lol get that cold air in should help a lot. It was last Nov Dec In my 2.4m x 1.2m I had 3 600's on a 8" rvk L1 with passive intake from open window and it was 24c at canopy with lights 12" above canopy. The size of your diy room is playing a part in this, if I remember correctly it's a monster room you've created ha Hope you get it sorted buddy

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My intake is run  from outside air, shaded part of the building, so its as cool as its gonna get.

Ive decided that im going with the aircooled hoods. Just down one side of the room tho, 

Im fed up with them on 400w already. the temps are still 27-29 under 400watts per light

The ones under the RDWC will be on open shades at 600W (because the water in the system is run through a chiller)

The bubbler plants will be under glass. I know its far from ideal, but I need to keep the temps a bit lower, and this is gonna be the cheapest option for me just now.

Thanks for the replies

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Can you add another intake onto the controller that set at 40% or is that a single controller ?


You have lots of power taking out and not alot coming in (compared to each other) you have 2600m3 going out and 750m3 coming in...you need that intake around 1000m3 in my opinion to have that even balance so you can run your 2,400w of lighting , 2600m3 is more than ample to handle that heat source so its the volume of air being replaced that needs increasing.


I would also consider running your intake ducting all around the perimeter of the tent with holes every 500mm for an even dispersal .



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What about adding a passive intake?

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On 05/09/2018 at 0:01 PM, badbillybob said:

this is gonna be the cheapest option for me just now.


Here's a cheaper one........


Looking at the balance between your m3 in and m3 out, I would say it's like trying to suck a McD's milkshake bud...........

Do what Rampa says above, chuck in some passive intakes and I reckon you'll see a huge difference......:yep:

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After buying the aircooled hoods, it turns out that thanks to the temp drop, I don't need them now, oh great...…


I need a smaller intake than extract for negative pressure, as the controller works both fans at the same percentage 

Ive turned the "constantly on" extract fan to a minimum setting, its literally turning over doijng nothing, so  I might even just turn it off altogether to be honest, save burning out the motor.

the other intake and exhause are working away fine off the controller, on idle, (40%) they havnt ramped up for days. 


its ok now. ive adjusted the settings on the variac controller  to get a good air exchange at idle, and the temps are sitting solid at 23-26 degrees. 

Ive not put the aircooled shades in because I am only working 4 lights (at 600w on open shades) and its coping well. It would probably be too cold if I set up the aircooled numbers. 

I should have listened to Owderb. Doh!


I might add another light for flower, but its not really necessary. if they get big I will hang it vertically, as ive had good results doing that before,


Ironically I was suffering from too low lights off temps this week, till I wired up the heater...typical eh?


Thanks for your iinput fellas, much appreciated

Edited by badbillybob
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Get air-cooled hoods next spring. Any loss in light through the glass is easily made up for by having perfect climate and by being able to allow the plants to get nearer the light.

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ive already bought them Milfslayer (great username by the way).

they are sitting in boxes in the corner of the groom.

might be needed in summer I suppose, handy to have.

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