Confused intake hole

T

temple balls

Active Member
And no this is nothing to do with any sexual references.

Ok building a grow room and have been looking at extraction fans what air movement ..... etc

Passive intake has got me confused, i have a small grow room 4ft x 5ft x 5.5ft and use a 8inch extraction fan but my passive intake is only 6inch.

The confusion is nearly every post of advice i have read is saying i should have a hole 3 times as big as my extraction or have more than 1 intake hole ?
The reason i made my hole smaller was to create a negative air pressure to suck out my stale air and it works so im confused.

Unless i experiment and make another hole to compare im not sure on the design of the bigger grow room.
If anyone who has experience on passive intakes i would be interested because im not sure by making the intake hole much bigger than the extracted one how can it efficiently exchange the air ?

Please educated me on this matter before i have to
a. make more or bigger intake holes
b. go round filling them in
 
Hiya temple balls. You are correct, that will be alright and you will get negative pressure.
Best way to find out is to run your room without any plants in it. You're mainly trying to run a good temperature with the lights on. So fire up the lights, switch the fan on and see how it runs and what the temps are like.
If you get to much negative pressure, ie: the walls of the tent suck in too much, then you can turn your fan down slightly or open the passive intake more.
The temp is the important thing.
 
I am not sure where the idea of smaller intake vs extraction holes idea originated but the difference in hole sizes will change the pressure slightly but why bother unless you are trying to hide aromas?

If “smell” is not a concern for you, then the difference in hole size will also create a difference in flow velocity. With a smaller intake hole, the flow through it will be faster than that through the extraction.

The biggest reason for a extraction fan is for air exchange and you have a room that is 110 cubic feet, so any fan moving more than that (4” fan runs about 110 cfm ) will exchange the air in a minute or less which is lots.

As smell is not a concern for me, I use a positive pressure setup in my tents, my fans blow into the top and exhaust through vents in the bottom. This blows the sides of my tent out a bit giving the plants near the walls a bit extra room and creates enough flow that I don’t require an oscillating fan in the tent .

Few thoughts for you to consider, there are many ways to set this up, but the most important is air exchange.
 
Thanks for your feedback.
Yes smell is an issue.
New room size is 1.8 x 3.0 x 1.6 but my focus 1.2 x 2.4 (grow area)
Cant afford Led's at the moment so heat off my lights is the main issue running two 315W cdm which acts as a heater in winter and a no grow in summer
 
Turn those lights on and see how it runs, like I was saying you may have to turn the fan down as it's so big, do you have a controller for the fan?
I run an oversized fan on my flowering room, I run it at half speed or less, very efficient and quiet.
You can run the lights through the night when it's cooler.
 
Random thoughts.

When I was building my grow I kept reading that the passive intake vent should be smaller than the out-vent. So for several years I ran the setup with an 8 inch vent/cooling fan and a 6 inch intake.

A couple years ago I got a new 10 inch fan and put in 10 inch ducting for it. The fan has a lot of power and it was difficult to open the door to the flowering room when it was running. But I also noticed (eventually) that it was pretty damn noisy with the door closed.

It fooled me for a while, because it would seem quite quiet in the room, then I’d close the door and walk outside and listen and it was noisy as hell. I figured out that the fan. was straining to pull enough air through that 6 inch hole.
I rebuilt the passive intake to 12 inches and everything became way quieter, and the cooling fan is coming on much less and working much less when it does.
 
im using Control freak fusion which in some sort of fashion changes the speed of the fan according to temp.
It can only cool the room efficiently when its cold outside. You can suck the paint off the walls put it wont cool the room down if its warm outside.
I'm using a RVK has two speeds but to noisy so was looking into buying a hyper fan with a silencer to save on energy.

Is installing a fan to blow the air into a room this small over kill or does it help with the extraction ? (3 x 2 x 1.8m)

One extraction fan say 6 inch or two 4 inch fans 1 for extraction other for intake
 
Hey Weasecracker may i ask did it still maintain odourless ?
If it did i think im going to be inclined to make it the same size
 
If the air isn't cool enough in the first place you are right ,doesn't matter how much air you pull through.
The only other options are to cool the air with ac,or go with led.
 
When im rich enough im going to run led's in the warmer months and my CDM's in winter ones.
Strange when the lights are off and say its 20c outside and its pulling air through gently its still 25c in the room what are they doing in there having a rave ?
 
temple balls said:
When im rich enough im going to run led's in the warmer months and my CDM's in winter ones.
Strange when the lights are off and say its 20c outside and its pulling air through gently its still 25c in the room what are they doing in there having a rave ?
Click to expand...
lol,Yeah, I run hps in the winter, to hot in summer so I grow in the sunshine.
I'm looking at the Samsung qb so I can run in autumn, I think it would still be to warm for me to run them still in summer without ac. Sounds like you've got a similar environment to me.
 
Intake size is about reducing load on the fan and most importantly as already noted reducing noise. The more air confined in a space the louder it is. Larger duct is quieter and more efficient. There's obviously an upper limit to it. Too large and you lose static pressure. Static pressure is felt as "push/pull" from the fan. Taping string at the end of duct is an easy indicator for making changes. It also costs more so no real reason to use drastically oversized.
 
temple balls said:
When im rich enough im going to run led's in the warmer months and my CDM's in winter ones.
Strange when the lights are off and say its 20c outside and its pulling air through gently its still 25c in the room what are they doing in there having a rave ?
Click to expand...


This is because your intake opening is too small. You can't pull enough air through it quickly enough.
With enough airflow you could maintain a space within .5°c of incoming air. It would be a buttload of air though.
 
temple balls said:
Hey Weasecracker may i ask did it still maintain odourless ?
If it did i think im going to be inclined to make it the same size
Click to expand...

Yes. I’m running a 10” Hyper fan in an 8 x 8’ flowering room, which is overkill on the fan size I suppose, but I wanted to be able to dim it down to a slow speed. I have a carbon filter on it of course, and the passive intake vent has a cover that sucks open when the fan is going, and springs back shut when it’s not. This vent cover works well. I guess it was part of some ducting setup in the past- something I was lucky enough to find in my local boneyard here.

The setup is low enough smell and noise for me. There are very subtle signs that the grow is there because I know it’s there, but for anyone else they would never notice. If it wasn’t good enough I would just work on it more until it was.

I can detect a slight hum when the fan kicks on. Perhaps a dehumifier would be good? But where to get one....
I would like to try some insulated ducting someday for the out-vent, which may or may not help with the hum.
 
Weaselcracker said:
Yes. I’m running a 10” Hyper fan in an 8 x 8’ flowering room, which is overkill on the fan size I suppose, but I wanted to be able to dim it down to a slow speed. I have a carbon filter on it of course, and the passive intake vent has a cover that sucks open when the fan is going, and springs back shut when it’s not. This vent cover works well. I guess it was part of some ducting setup in the past- something I was lucky enough to find in my local boneyard here.

The setup is low enough smell and noise for me. There are very subtle signs that the grow is there because I know it’s there, but for anyone else they would never notice. If it wasn’t good enough I would just work on it more until it was.

I can detect a slight hum when the fan kicks on. Perhaps a dehumifier would be good? But where to get one....
I would like to try some insulated ducting someday for the out-vent, which may or may not help with the hum.
Click to expand...

I use an 8" hyperfan on two 4*4 tents with a pair of 8*24 filters. It's no louder than my furnace unless your in the room with them. You can usually hear the waterfall in the res over the air movement. I can keep my tents within a couple degrees Fahrenheit of ambient temps if I run it full speed. I use the hyperfan temperature controller and I love it. I have two of them.
 

Similar threads

Black Thumb
Intake Freezing winter air ?
Replies
1
Views
779
Fuzzy Duck
Fuzzy Duck
D
Passive intake
Replies
6
Views
2K
PrairiePoet
PrairiePoet
E
Tent sucking
Replies
6
Views
640
Listersmeghead
L
T
Exhaust in right position?
Replies
17
Views
1K
Rexer
Rexer
coralman
Portable A/C unit help
Replies
2
Views
1K
coralman
coralman
Back
Top Bottom