Push Pull: Which fans to push and which fans to pull?

Frank Jeagar · 10 Dec 2015 at 18:38

My question is what is the benefit of putting fans with different characteristics (i.e. air flow and static pressure) on either the push or the pull side of the rad?

As I understand it, static pressure helps most when there is an obstruction on the side the fan is pulling air from, so static pressure optimised fans would surely be best at pulling through the rad, right?

If I put fans that have high air flow as push fans, would this be beneficial or not or just negligible compared to static pressure fans?

I also heard people saying that having fans that don't move enough air on the push side of the rad could choke the pull fans, but I would have thought that if the air is being pulled through a rad that a fan on the other side wouldn't really increase resistance much even if it is off, let alone if it is spinning and pushing air...

Thought this debate might be somewhat interesting

Uncle Petey · 10 Dec 2015 at 23:33

Considering that the benefits of push pull are negligible to begin with, I'd say not to worry about it

VKleita · 11 Dec 2015 at 00:18

Uncle Petey tells the truth as always.

Everything I have read seems to indicate to have matching fans, otherwise either one fan is pushing or dragging the other one anyway.

Having had a 280 Rad and tried it , push then pull and push-Pull I have to say I have seen very little difference tbh, push pull made it a arse to dust the rad thou.

Frank Jeagar · 11 Dec 2015 at 09:31

Uncle Petey said:
Considering that the benefits of push pull are negligible to begin with, I'd say not to worry about it

Haha, good point, a lot of debate over nothing!

I'll be honest, the only reason I am using push pull is because I want some nice led fans to show through my front filter and then some strong fans on the inside to actually provide cooling haha

bimbleuk · 11 Dec 2015 at 09:43

I messed with some rad setups in my case (CPU & GPU AIO coolers) and now I just push with high static pressure fans. Reduces the interaction of two fans spinning at different speeds in close proximity.

I reckon you'll get more of a temp difference switching the direction between intake or outake.

Glanza · 11 Dec 2015 at 11:21

Unless your running Monsta rads push pull isn't required.

Uncle Petey · 11 Dec 2015 at 12:04

Tbh, I ran Monsta rads for a while and found that push pull made more difference psychologically, though it did help with keeping fan speeds a bit lower rather than provide any meaningful temp drop beyond the usual 2-3°C or so.

They're fairly low FPI anyway.

BluD · 11 Dec 2015 at 13:49

Gonna say its all down to FPI aint it?, ive always used thick low fpi rads and low static pressure fans on push or pull depending where theyre mounted. I tried some high SP fans to see if it cooled it better but all it did is make it noisier.

Ive never tried high FPI rads but i imagine using push/pull on them would just allow you to run the fans a little slower for less noise, although i thought the whole point of high FPI thin rads was to fit them into smaller spaces which using push/pull on then kind of defeats the point.

Frank Jeagar · 11 Dec 2015 at 14:39

Okay, fresh question:

If I have 2 fans pushing air through a rad at low rpm to keep noise down will it at all hinder the fans pulling through the rad on the other side?

Surely the resistance added by the fans is negligible October,pared to the resistance of the radiator and any air they push in will provide a benefit however small it may be?

Uncle Petey · 11 Dec 2015 at 14:54

Seriously mate, it's not worth over analysing this stuff.
If your temps are good and you're fine with the noise level, leave it alone and be happy

Frank Jeagar · 11 Dec 2015 at 15:39

Uncle Petey said:
Seriously mate, it's not worth over analysing this stuff.
If your temps are good and you're fine with the noise level, leave it alone and be happy

I feel like this sentence should be said more in forums

I like the look, I can't feel any air flow drop with my hand, therefore it they are staying!

Thanks, the discussion was interesting everyone

ttaskmaster · 11 Dec 2015 at 15:50

Frank Jeagar said:
Surely the resistance added by the fans is negligible October,pared to the resistance of the radiator and any air they push in will provide a benefit however small it may be?

Nope.
I have actually busted a fan doing this incorrectly. First time I did it, the compression popped the fan off its spindle (it was designed to come off for cleaning anyway). Later on I swapped the fans around and the slower fan in Pull caused a compression stall that threw the blade on the faster Push one and caused it to chew the bearing, before dying outright in very short order.

Frank Jeagar said:
As I understand it, static pressure helps most when there is an obstruction on the side the fan is pulling air from, so static pressure optimised fans would surely be best at pulling through the rad, right?

Pushing or pulling, yes. SP isn't better in one that the other. It's just down to preference.

The one exception is if you're using Enermax fans with the additional side intakes, in which case they are best in Push only. No point Pulling, as half the air they move will not be coming through the rad.

Frank Jeagar said:
If I put fans that have high air flow as push fans, would this be beneficial or not or just negligible compared to static pressure fans?

Generally it will be worse, as all that airflow lacks the force to go through the obstruction.

Frank Jeagar said:
I also heard people saying that having fans that don't move enough air on the push side of the rad could choke the pull fans, but I would have thought that if the air is being pulled through a rad that a fan on the other side wouldn't really increase resistance much even if it is off, let alone if it is spinning and pushing air...

It creates a vacuum in the airspace between the two fans. You force the slower one to go faster while dragging the faster one back as if you were holding it with a finger.

Frank Jeagar said:
My question is what is the benefit of putting fans with different characteristics (i.e. air flow and static pressure) on either the push or the pull side of the rad?

The benefit is that you knacker your fans and have to buy more, which makes more money for the retailer.

There is no benefit for you, really.
You get a bit less of a problem if an SP fan is pushing into an Airflow pulling, but it helps if they are running around the same rpm and are decent with both CFM and SP values.
Mixing speeds is worse, as you can cause a compression stall, which is what buggers up the bearing and kills the fan.
Best bet is SP fans in both push and pull, running at the same rpm.

Worth noting that Push-Pull is generally better by a small, but measurable amount.
There is no difference between Push or Pull, except that Push traps a lot more dust between fan and rad.