Push, pull and push/pull: erm, what?
16.6.2019
Responsibility for translation Eva Francis
AIOs – all-in-one coolers – are the entry point to liquid coolers for your PC. They’re quick to assemble and they don’t need much upkeep. While they are fairly basic compared with custom water cooling systems, they do have certain similarities, including the impact of fan placement on cooling efficiency.
Push, pull or push/pull – which is better?
User khrys_neotk got themselves the Kraken x62, an NZXT AIO. In the subsequent review, he explains that he set up a push/pull configuration. This helped him to reduce the average temperature by about nine degrees. If you don’t know what that means, don’t worry. I’ll explain in a minute.
Khrys_neotk’s comment snagged him a spot in our Community ad campaign. Even I’m intrigued now and want to know what impact the fan position had on the AIO’s cooling performance.
Push, pull or push/pull after all?
You can attach fans to both sides of the radiators. When the fans are placed in front of the radiator and air pushes through them it’s called «push». If, however, the fans are behind the radiator and they pull the air through them, that’s called «pull». And when the fans are placed behind and in front of the radiator, that’s known as a push/pull configuration. In that scenario, the front fans push the air through the radiator while the rear fans pull the air through.
The more air that’s pushed through the slats of the radiator, the better this will then cool the liquid in the water cooling system. On paper, a push/pull configuration is therefore the most efficient. That’s especially the case with thicker radiators and/or those with slats that are very close to each other. If that’s the situation you’re looking at, you’ll need more static push to transport fresh air through the radiator. But it goes without saying that this isn’t the only factor that affects the cooling efficiency of a water cooling system. The size of the radiator also plays a significant part. Wider and thicker radiators provide more surface area and can therefore cool better. In this instance, bigger really is better.
With an out-of-the-box AIO, the options are limited. It’s not like you can just extend them. You’re stuck with the size you initially bought. So if you decide you want to improve the cooling efficiency of an AIO, you don’t have much option other than a push/pull configuration. That is, if you have space for it in the casing. But what I want to know is how much a push-pull set-up really helps.
The test set-up
I tested out all three configurations on my colleague Philipp Rüegg’s streaming PC to see the effect the fan arrangement has on cooling efficiency. In the process, I cooled a Ryzen 7 2700X with a Kraken x52 – the younger sibling of the Kraken x62. You can find all the system components here. The Kraken x52 comes with a 240 radiator and two 120 mm fans. The Kraken x62 meanwhile boasts a 280 radiator with two 140 mm fans. Greater surface area on the x62 results in more draught compared with the x52.
This difference is pretty trivial for the test in question. But you can assume the results from the x62 are similar, just with lower temperatures. For this test I’m using the Stresstest Heavyload. And I just select the option to take the processor to its performance limit. All eight cores of the Ryzen 7 2700X are stretched to capacity within ten minutes in the 23°C office. I choose ten minutes because the temperature levels off after about five minutes and doesn’t increase. The two 120 mm fans on the radiator are running at 1,000 of a possible 1,500 rpm.
For the push and pull tests, I reach for the accompanying NZXT fans. As I only have two of these, I add an additional two Corsair LL120 fans for the push/pull configuration.
Airflow is always restricted by the casing. That’s why I place the radiator along with the fans next to the casing. This way I eliminate the housing as a limiting factor for the airflow. If I were to carry out the test inside the housing, this could affect the results. Depending on the casing involved, a push or pull set-up can be better for the cooling performance of the water cooling system. But I want to test independently of the casing.
The test results
The test yields the results I expected. The push/pull configuration is the most effective way to cool the Ryzen 7 2700X. And there are three degrees difference between the entire push and pull set-up:
Pull: 58°C
Push: 55°C
Push/pull: 53°C
Bear in mind that the temperature differences could be greater depending on the casing. User khrys_neotk explained that he managed to drop the temperature by nine degrees when he used the push/pull set-up. I imagine that it also had something to do with the housing. Perhaps the fans couldn’t pull enough air.
It’s clear to me upon completing the test that push is more efficient than pull. If you think about it, the fans can push air from all directions but with pull they can only drag air from in front through the radiator.
While I’m putting the set-up through its paces, I also check to see how the temperatures fare in the test scenario with the in-built radiator in the casing in a push configuration. As it happens, the casing does indeed play a big role: at 62°C, the temperature is seven degrees higher than with the push configuration outside of the housing.
Side note: in his review, user khrys_neotk also advises against building the radiator into the front of the casing. This is because he thinks the warm air from the radiator heats the casing even more. I’m sorry to disagree with khrys_neotk but that’s not right at all. In fact, in most cases it’s even better to attach the radiator at the front.
In this YouTube video you can see Kyle Hansen from Bitwit test out the impact of radiator placement on the temperature. He discovers that heat loss from the radiator in those attached at the front doesn’t have much of an effect. The temperature that goes inside is still lower than the temperature within the housing as a result of heat loss from components. His results show that radiators attached at the top can actually cool less efficiently than those mounted at the front.
Kevin Hofer
Senior Editor
kevin.hofer@digitecgalaxus.chFrom big data to big brother, Cyborgs to Sci-Fi. All aspects of technology and society fascinate me.
