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Carbon filters, Do you push through or pull?

A

AnonMe

Active member
Never had the need to run one, but might have to soon. Had a scout around at a few brands etc. Spoke to a few shop owners and one guy was insistant that you should be pushing through them.

At the time it kind of made sense because I've worked with pumps before (a bit like a fan) and I know the suction head is always less. Like a pump might have 40m of head at the discharge end, yet only 8m of head at the suction.

However, reading around some people have said you should always pull through the filter because there is a prefilter on the outside. I am interested in what people here do. I think the majority of you pull through. Any pushers?

I think its important to note, the shop owner was saying put the fan+filter together with no ducting between up in my roof space.

Here are my two options for setting up my next grow. Any advice?

===== Ducting
X fan
O filter

Option A:
(Tent OX==)============(== Roof space)
or
Option B:
(Tent ===)=============(==XO Roof space)
 
W

willyweed

filter (carbon) ==== fan (mixed flow are quiet ) ========== ducting out of tent or room
there is a warning on most filters to say this .all the best.ww
if you pull through the filter ,it will last a lot longer than doing it the other way around,also with pulling through the filter the pre filter will take out most of the large dust particles first !
 
G

Granger2

Active member
Veteran
Anonme,
I have no interest in getting into yet another argument about push vs. pull. I'll leave that ongoing argument to the 2 camps of engineers who continue to go at it. I will state my preference and others are free to do the same.

Whenever possible I prefer pulling air thru the filter, if for no other reason than you get a lot more prefilter surface area.

I prefer Phresh filters. This may help. Can makes good products, but I've never owned one. They have a good FAQ here: http://canfilters.com/faq.html
Always get a filter with a higher CFM rating than your fan. Good luck. -granger
 
Treetroit City

Treetroit City

Moderately Super
Veteran
I agree they should be pulled from.

Just think about the word "prefilter". Pre being before, so it is there to filter before the carbon.

If you are pushing through your filter it would be a postfilter. Don't know about you but I've never heard of the prefilter referred to as a postfilter.
 
GrowerGoneWild

GrowerGoneWild

Active member
Veteran
I think pulling is better heres my reasons..

1) The speed of the air is slower, on an intake side so the carbon has more time to work on the air.

2) It seems to load up the fan, especially if you run panasonic whisper fans, and it makes noise. Thats why you pull instead of pushing air into a can.

3)I sometimes run ozone, so that goes on the exhaust side to the outside.
 
Last edited:
intotheunknown

intotheunknown

Active member
Veteran
pull.

easier to find stink/air leaks in your ducting.
less chance of stink getting out.

pull>>>scrubber>>>>hood>>>fan>>>exhaust>>>>
 
A

AnonMe

Active member
Hello everyone,

Thanks for all the replies. Looks like pulling wins. I was kind of looking forward to mounting the fan/filter in the roof. I think it would be a bit quieter up there.

I'm going to get a 2.4 x 1.2 x 2.0m tent with 2 or 3 600watt globes (depending on how it looks/fits) and was thinking of going the Max-Fan200 with a cann30 or cann50 filter. I'm hoping it will be silent enough at the end of the hallway behind a door, and inside a tent.

Value all your advice. Cheers!
 
N

noyd666

there is phresh filter u-tube site that shows folding the prefilter to fit inside the main filter so it cleans some bigger particals before exiting scrubber if pulling air through= reverse the other way . grower's house .com. video said PHRESH FILTERS CAN BE USED PUSH OR PULL. USING TWO AN NO PROBLEMS SO FAR.
 
e_24

e_24

Active member
I push I bought a filter way to big for my environment. I used to use a phresh with the filter up front, then needed more room in the grow and places it on the push side where it didn't work too well and I got quite a bit of blow by. When I upgraded filters, it was time, I got one rated for a tent 3x the size of mine. No more blow by, and the tent is cooler with less restriction on the intake side.


Just note that I had to use a filter 3x the recomended size for pushing air through.
 
T

The Gator

Member
I would go with option A. Pulling through your filter allows your pre-filter to capture dust and particulates and it also allows for greater media contact since you are pulling air from all sides of your filter, instead of pushing air through one opening.
 
T

ThcGrower4life

i think carbon filters are made too be pulled through as the come with a filter sleeve
 
Picarus

Picarus

Member
Push. No one has mentioned that humidity renders the carbon inactive. Having it inside the room crowds the space, needs to be replaced faster (more dirt and dust), and with high humidity it can become less effective. Good Luck!
 
qupee

qupee

Member
Do whatever works for your space/setup. Both push and pull work fine.

AnonMe said:
Like a pump might have 40m of head at the discharge end, yet only 8m of head at the suction.
Click to expand...

Centrifugal fans don't have that imbalance. With an appropriate length of straight duct off each end of the fan, there is no difference.

Picarus said:
Push. No one has mentioned that humidity renders the carbon inactive. Having it inside the room crowds the space, needs to be replaced faster (more dirt and dust), and with high humidity it can become less effective. Good Luck!
Click to expand...

This is very true, however a minor point.

intotheunknown said:
pull>>>scrubber>>>>hood>>>fan>>>exhaust>>>>
Click to expand...

This is a poor way to arrange things. The fan will pull unfiltered air into the line after the scrubber through gaps in your hood. In any arrangement, you want as few potential leaks as possible between the fan and filter or you risk expelling unfiltered air (when pushing, only potential leaks outside of your filtered space are of concern).

GrowerGoneWild said:
1) The speed of the air is slower, on an intake side so the carbon has more time to work on the air.
Click to expand...

The air will be moving the same speed at the outer surface of the filter regardless of which way the air is moving. Why would it be slower pulling? In both cases the same volume of air is traveling through the same change in area. The air flow speeds up as it travels through when pulling, just the same as it slows down when it travels through when pushing. It is exactly the same through the filter. Same time in contact, same amount in contact. This is simple fluid dynamics.

Use a prefilter when pushing, the only neg is that you'll have to clean/change it more frequently due to the (most likely) smaller size.
 
GrowerGoneWild

GrowerGoneWild

Active member
Veteran
qupee said:
The air will be moving the same speed at the outer surface of the filter regardless of which way the air is moving. Why would it be slower pulling? In both cases the same volume of air is traveling through the same change in area. The air flow speeds up as it travels through when pulling, just the same as it slows down when it travels through when pushing. It is exactly the same through the filter. Same time in contact, same amount in contact. This is simple fluid dynamics.

Use a prefilter when pushing, the only neg is that you'll have to clean/change it more frequently due to the (most likely) smaller size.
Click to expand...

Wrong. its not like fluid.. Fluid does not compress, thats hydraulics.
There is compression with a fan.

So I can say that there is compression in an air blower/centrifugal system.. thats a fact.

I'll go with a conservative estimate of 1:2 compression ratio. So you're trying to force more air through a filter.. So that in theory should be moving air faster over the filter.. not such a good idea for something that uses adsorption. you would have to make up for it with higher air recycling rates or more surface area.

Observations:
My HEPA filter for the house uses a carbon filter on the suction side of the unit. What you suggest is opposite of a commercial design.

Lastly, there is much less surface area the air first contacts for the if you push into the can. Take the internal diameter of the can and do a cylinder surface area calculation, then take the OD of the can and do a cylinder surface area calc.

I got my own reason why I pull.. Now Im sure there are valid reasons for pushing but unless somebody explicitly explains it correctly with facts and observations I'll go with that.
 
whadeezlrg

whadeezlrg

Just Say Grow
Veteran
intotheunknown said:
the bigger, the better. overkill it on both ends. fan and scrubber. and get a fan speed controller.
Click to expand...

^^^this, why debate on push vs pull when having a filter on each end is the easiest way to eliminate ALL odors?

seriously ALL of em, no smell at all. I used to pull through a single filter and would have smell issues immediately after the lights would shut off (just briefly, but it had some generally had some kick to it) added a second filter and haven't had a smell issue since(3+yrs)...wouldn't think about running a different way.
 
Chunkypigs

Chunkypigs

passing the gas
Veteran
both ways work fine. with tents I like the filter standing up outside on the floor with the fan on top blowing into the filter. hose from fan to tent sucking out the heat and stink. this setup frees lots of room when your plants get tall. you can use one big 12" filter and fan to vacuum 2 or more small tents.
 
N

noyd666

I see phresh has new =HYPERFAN OUT MADE FOR PUSHING OR PULLING WITH REMOTE SPEED CONTROL.
 
Applesauce

Applesauce

Member
I pull through the carbon filter but push through the lighting in an effort to reduce high heat going through the inline fans.
 
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