Exhuast size for 125mm ducting

[howajepayle]

Hi folks, I am building an NGB style dresser, and I ahve 125mm ducting from my cool tube (which is now broke but never mind!), anyway, should i have the ducting runnign to the side of the box, and jsut cut a 125mm hole? or a slightly smaller hole (and hope the air flow isnt too restricited). i have 3 passive intake pipes, each about 2 inches in diameter. altogether , does that mke a 6" intake? and does that mean i can only havve a 3" exhaust hole? or does it not matter. please help, im gonig to finish this tonight!!!!!!!!!! (hopefully)

 

[howajepayle]

just realised, this might be a stupid question, i.e. the answer being my exhaust has to be 125 mm , and my passive intake 250mm. this would mean anoth 2 passive intake pipes, but i cant afford the little s-bends or whatever they are called. should i just drill a 125mm hole in the side and put my ducting out there? that owuld leave me with 5"exhaust and 6" intake. im arunnign a 250w hps. might put a 200w cfl in too. please guys, i have to get this box ready tomorrow morning!

 

[EddieShoestring]

should i have the ducting runnign to the side of the box, and jsut cut a 125mm hole?

yeah-
actually it's a good idea to have the vent hole for the cooltube slightly above the level at which you are going to use the tube-as the warm air wants to go up anyway-

otherwise- No, 3 2inch cirles don't have the same area as a 6" circle-can't remember the formula tho
good luck
eddie

 

[Guest]

Try this figure: a 2" circle has a surface area of 9.86 sq inches
a 6" circle has a surface area of 88.7 sq inches

Translated is it would take 8.9959432 (2 inch) circles to equal a 6" circle.

BigNugget you are correct. They say Pi x r2 I say Pi are round and cornbread are square.

Happy Growing and Peace

 

[howajepayle]

thanks guys, a nobel prize for mathematics is winging its way as we speak


do i HAVE to have twice the exhaust? i dont know how im going to fit all this holes in ! i have 3 now, and they take a bit of room -ive only a little cab. i have them in the floor at the side aat the mo, should i spread them around the floor?

plus, as my exhaust is 125mm (5" i think), does tha tmean i have to have a 10" intake? im getting confused (its late, not had a j for a few days ) you might have already given me details for this. but i should be able to work it out. in the end...........

 

[EddieShoestring]

if you've got a active 5" extractor then you'll need 2, or better 3, 5" passive intakes-
if thats a problem get a fan on the intake

eddie

 

[howajepayle]

how about ana active intake with either a pc fan or another smaller inline fan? the inline fan i could hook up to my thermo-fan speed controller, but how would i light proof it? just ahve it sticknig out fof the side, with ducting wrapped for light proofing? or how could i make a light proof acticve intake witha comp fan?


if i have an active vent, should i keep the apssive intakes? would they negatively affect things (negative pressure etc.)

thanks for the help so far, as soon as i work out the rep system i will send some all your way

 

[EddieShoestring]

alright mate

how about ana active intake with either a pc fan or another smaller inline fan? the inline fan i could hook up to my thermo-fan speed controller,

good idea

but how would i light proof it

with a length of ducting, as you said-or rig up some sort of light trap. It travels in straight lines so is easy to trap-matt black surfaces are good. But remember the more interuptions to the airflow (ie bends or boxes) the more the flow is impeeded.

Ideally you would have a slightly less powerfull fan on the intake-but if you go for a low power thing like a pc fan then having some passive vents as well would be cool

as soon as i work out the rep system i will send some all your way

lol-took me over 6 months

cheers
eddie

 

[howajepayle]

ive got a 160 td inline fan, gonig to hook it up to fan spped controller, but not srue what directino is best for the intake fan to be blowign, i.e. should it be positioned horizontally or vertically? im going to situate it at the opposite bottom corner to the side where the carbon filter is. should i have the fan just poknig through the floor, or through the side (hope you know what im getting at )

also, with my temperature controlled fan speed, should i set the 'idling times' or whatever for the fan very low, so that when it reaches the desired temp, they turn down to that very low setting? or have it in the middle of the range.. doesnt seem to make much diff with noise (no increased humming , or at least not much, at the lower settigns)

 

[EddieShoestring]

i'm not sure that vertical-or horizintal makes any diff-horizontal if poss

otherwise-you'll just have to experiment with the settings of your controller and see what actually happens to the temps-then adjust etc

eddie