Fan cfm ratings question

Michael Willis · 4 Jul 2018 at 09:13

Hi all, I've just built a computer and I want to get optimal airflow around my case..

I have been told that the airflow being pulled in to the case should equate to the same total cfm to the airflow being exhausted out of the case.. Is this true?

Also to help determine the above problem.. Does anyone know of any software which will show you the cfm rating of fans as my case come with 4 stock fans but no info on their cfm.

The fans are 1x 80mm and 3x 120mm

The case is the NZXT Lexa Blackline

Thanks guys

Mike

Rroff · 4 Jul 2018 at 09:22

Unless you have a perfectly sealed case where all air is coming and going via the fans perfectly matching CFM isn't essential. People tend to bias towards having a slightly higher inflow so that dust isn't drawn in via unfiltered holes in the case and/or tends to be pushed out.

Michael Willis · 4 Jul 2018 at 09:47

Hi rroff thanks for your reply.

You see this is the same thinking as what I originally thought.. Common sense dictates that if you have more airflow entering the case than being expelled, the intake will help push warm air out of the case faster keeping it cooler..

Ad_Augendae · 4 Jul 2018 at 14:01

I think the balance of airflow/expense vs fan noise is a factor to consider. lower intake more dust less noise vs higher intake less dust more noise.
Not forgetting the cooling bit

A good example would be that I bought a case with high airflow an RL06, works great keeps it all cool but the fans resonate with a horrid pitch at fulll tilt.
I had to change plan and throw in 2X 120mm noctua intead (might as well of spent the extra in the first place). Be wise with fan choice if your going for big airflow.

doyll · 4 Jul 2018 at 14:15

Michael Willis said:
Hi all, I've just built a computer and I want to get optimal airflow around my case..

I have been told that the airflow being pulled in to the case should equate to the same total cfm to the airflow being exhausted out of the case.. Is this true?

Also to help determine the above problem.. Does anyone know of any software which will show you the cfm rating of fans as my case come with 4 stock fans but no info on their cfm.

The fans are 1x 80mm and 3x 120mm

The case is the NZXT Lexa Blackline

Thanks guys

Mike

Yes, it is true, but unless case is a pressure tank the intake and exhaust flow rate will always be the same .. hopefully the below will explain why and how.

First a basic tutorial as to how airflow works. Whatever air goes into a case has to come out. Think of a case as a tank and air as water. The tank is already full of air/water, so putting more in means the same amount has to come out. Below is a link to more detail as well as a basic tutorial of how to setup case airflow
https://forums.overclockers.co.uk/t...-i-put-my-temp-sensor.18564223/#post-26159770

Ideally we want the intake and exhaust venting are to be equal or exhaust a little bigger. The number of intake vents with fans has to be less than the number of exhaust vents.

Fan airflow and pressure specs are grossly misleading. a fan rated 70cfm is measured with same pressure on both sides of fan being exactly the same .. but in order for a fan to move air in actual use there is more pressure on exhaust side of fan than intake because the fan is pulling air in from intake side creating lower pressure close to fan and pushing air out exhaust side creating higher pressure.

This pressure differential is what creates airflow.

Fan static pressure rating is the amount of pressure fan is making when it stops flowng air .. static = stopped .. fan is mounted to a sealed container and ran at full speed, then the pressure inside of that container is measured.

Michael Willis · 4 Jul 2018 at 14:22

Thanks for the reply, I'm not necessarily going for massive amounts of airflow but I do want to keep it cool and avoid dust particularly I have 6 fans, that's 4 case mounted and 2 on the cpu heatsink on top of that your usual psu and gpu fans.. I am running the Asus B350 plus mobo, the ryzen 7 8 core 1800 processor and a sapphire rx 580 nitro+ graphics card with 2 sticks of Kingston fury white 16gb ddr4 ram

My fans all have dust filters too

Thanks also doll interesting read.. I didn't know about the difference in pressure from intake to. Exhaust

doyll · 4 Jul 2018 at 15:11

Good rule of thumb is to us as many intake (I generally don't even use exhaust fans because good pressure rated fans will push air right on through a case) as there are fans on coolers. So if your CPU cooler has a 120mm fan and GPU has 2x 80mm the ideal would be 3x 120mm intakes with at least 3x 120mm rear exhaust vents.

But your case is designed with 1x front, 1x side & 1x back 120mm vents and 1x 80mm top vent with PSU also functioning as an exhaust vent. You can greatly increase the rear vent area by removing all PCie back slot covers. This also massively increases front /side to back airflow airflow by giving you venting around GPU. Looking at pics of your case it looks like it's extremely limited airflow potential without extreme modding. HDD cage is very restrictive to front fan, side vent is only a few slits cut in plastic window. But at the end of the day your case just isn't a good airflow case. I would be looking at getting a new case because it will most likely take some serious modding to get needed airflow in what you have.

Are your temps running too hot now? What are they when gaming?

I think the best you can do without modding your case or changing cases is have very good top, front and side intakes with PCIe slot covers removed. In all honestly I would never get a case like yours, but it's what we have to work with.

Michael Willis · 4 Jul 2018 at 15:25

Interesting again, I'll remove the pcie slot covers, currently it's idling around 30-40 degrees on the cpu and same with gpu, hdd a few degrees lower, not had a chance to game yet only switched on for first time last night

Oh I also have the darkrock Pro 4 cpu cooler it has 2 fans 1 is 120mm the other is 130mm or something

doyll · 4 Jul 2018 at 15:32

30-40 sounds quite warm. For example my 6700k is at 25-33c depending on core in 23c room and case filters need cleaning

Michael Willis · 4 Jul 2018 at 16:29

Yeah but take into account ambient room temp at the mo is hot because of the weather.. I did read that a cpu should be sitting around 30-40 could also reach up to 80 without affecting performance..

doyll · 4 Jul 2018 at 16:57

Michael Willis said:
Yeah but take into account ambient room temp at the mo is hot because of the weather.. I did read that a cpu should be sitting around 30-40 could also reach up to 80 without affecting performance..

Well, here today it's only 23c out, but even if it is 27c idling at 40c is quite warm. Besides, idle temp and high load temps are very different beasts. My 25-33c low load is like 60-68c high load. If I'm just surfing web and answering posts my temp is 25-28c. To get that kind of idle to 40c my room would need to be about 35c .. and my load temp would be about 78-85c.

Basically every degree warmer the air into cooler is translates into a degree hotter CPU will be. My guess is your room air temp is low to mid 20s, but the air inside of your case going into your cooler is 10-15c hotter. So if room is 24 and we add 10 the air into cooler is 34c with CPU being 5-6c warmer.

I've seen many build where case airflow was not good having 20-35c higher case airflow temp into coolers than room when gaming .. all because the GPU heated exhaust was not being removed from case but instead was heating up the airflow. Stock down-flow/pancake CPU coolers also cause / contribute to this problem.

Michael Willis · 4 Jul 2018 at 17:11

So why your saying is the air needs to. Be exhausted from the cpu more, interesting although googling idle temps still ping back to me at in and around 30c.. However I'll have a look tonight when I can put it through its paces see what feedback I get

doyll · 4 Jul 2018 at 18:38

The heated air out of GPU and CPU needs to flow out of case without mixing with cool intake air going to cooler. Supplying coolers with cool air is the key.
Around 30c is fine. 40c is kinda hot for surfing.

EsaT · 5 Jul 2018 at 09:12

Michael Willis said:
The case is the NZXT Lexa Blackline

You should really show that outdated design already decade ago case some Dremel.

That restrictive stamped mesh for example in rear exhaust blocks lots of airflow or needs heavy for pressure for lots of noise.
http://www.overclockersclub.com/reviews/lexa_blackline/2.htm
https://www.techpowerup.com/reviews/NZXT/Lexa_Blackline/3.html
It along with case layout also makes PSU major exhaust forcing it to suck in lots of heat from components.

Also with front intake fan heavily restricted by HDD cage or some hole plate would cut proper hole for 12cm intake fan to bottom, unless that side fan can move decent amount of air.
http://www.overclockersclub.com/reviews/lexa_blackline/2.htm#&gid=1&pid=11990

Before taking care of of those airflow obstructions any fan swapping is "lipstick on a pig".

doyll · 5 Jul 2018 at 10:44

What EsaT said.
I'll be surprised even modding if your Lexa Blackline will as much airflow as is needed and remain quiet.
There are some good cases starting at about £60