Intake/Exhaust Questions

[jacktesterson]

Hi There,

I built this HTPC a couple months ago. Its a low profile setup. See the setup in the sig.

Here is a pic I took a few weeks back when I installed the new heatsink in the rig. (And I did some cable management after this, its cleaned up now. Video card that I used can be seen in the pic on the side as well).

I originally was using no case fans, and had a stock cooler from a FX-8350 (With the copper heatpipes) installed.

I was having a lot of fan noise. It seemed the fan was constantly running at 50% throttle, and would spike to 80-100% when doing something. AMD's stock 80mm fan wasn't very quiet and it drove me nuts.

So I installed 4 x AC Case fans (All are setup to be intake) and it helped quiet the Heatsink down a lot, but I could still hear it at times playing just video, and gaming would still crank the fan speed up.

So I purchased the large Heatsink as shown in the pic. Since then the setup is now very quiet and I never hear it even under load in almost all situations.

My question though is this..... Should all 4 of those side case fans be intake? Or should 1 of them be an exhaust? What would you do?

 

[Blain]

I'll assume the large CPU fan is blowing down onto the HS, which would require it to have a substantial opening for an intake port.
Given that configuration, I'd use the large CPU fan as an intake, and the four smaller fans as exhaust.

BTW, I've got the same case with only a single AC fan blowing down onto my CPU HS, no other fans, other than the 120mm PS fan sucking air into cool the PS.

 

[jacktesterson]

I'll assume the large CPU fan is blowing down onto the HS, which would require it to have a substantial opening for an intake port.
Given that configuration, I'd use the large CPU fan as an intake, and the four smaller fans as exhaust.

BTW, I've got the same case with only a single AC fan blowing down onto my CPU HS, no other fans, other than the 120mm PS fan sucking air into cool the PS.

Yes the large fan is blowing down, and the 4 side fans are all blowing air into the case.

Just a FYI the top cover has a huge grill over the top of the CPU cooler for air.

I should move all 4 to exhaust?

Thanks

 

[Valantar]

I doubt you'd gain anything from switching them to exhaust. If air needs to get out, it gets out. Plus, you can never have a too large supply of cool air.

 

[Blain]

At least the two fans at the rear should be blowing out.

 

[BonzaiDuck]

As far as airflow and cooling strategy are concerned, there should be no difference between an HTPC and a tower gaming PC for achieving cool and quiet. You just have less space to work with because the HTPC is likely to be compact.

there's an advantage with those 4 fans as intake: the less roomy the case, the better the airflow and cooling, the better you'll be able to pressurize the case. You just need enough exhaust to . . . help it along.

 

[Blain]

There's not going to be any appreciable "pressurization" of that case.
"Air flow" is what moves hot air out, not pressure.
Air flow is accomplished by a balance of intake and exhaust, while creating as little turbulence as possible.

 

[jacktesterson]

At least the two fans at the rear should be blowing out.

There is zero room for any more fans with the video card installed. (Even then I'd have to modify to get something in)

The only 4 spots for fans are what's shown in this pic.

Its a tiny case. It looks big in the Pic but its not.

 

[Blain]

There is zero room for any more fans with the video card installed. (Even then I'd have to modify to get something in)

The only 4 spots for fans are what's shown in this pic.

Its a tiny case. It looks big in the Pic but its not.

I totally, 100% got that. You have 2 towards the front of the case and two towards the rear of the case.

Front 2 = intake (blowing in)
Rear 2 = exhaust (blowing out)

 

[Ketchup]

I doubt you'd gain anything from switching them to exhaust. If air needs to get out, it gets out. Plus, you can never have a too large supply of cool air.

Actually, you have this backwards. Once in the case, hot air will just sit there unless it is redirected.

It is always a good idea to have more pressure going out than coming in. Air will flow in whatever direction air pressure tells it to go until it hits a barrier.

So if you have only intake, the hot air from the CPU will only warm the air brought in, and not escape due to all the barriers. If you have only exhaust, the air will be pulled from wherever there is an opening from the outside. If you want the air to hit a specific device (instead of just taking the shortest route), an intake fan should be used at that location.

 

[jacktesterson]

I totally, 100% got that. You have 2 towards the front of the case and two towards the rear of the case.

Front 2 = intake (blowing in)
Rear 2 = exhaust (blowing out)

Cool - I've been debating doing exactly this but wasn't sure it would be worthwhile.

 

[ClockHound]

Cool - I've been debating doing exactly this but wasn't sure it would be worthwhile.

Be interested to see what happens when you switch 2 of the intakes to exhaust since all the fans are mounted on the same side. Can't imagine getting much flow going, except straight in and out, bypassing the parts that need the flow. ;-)

Looks like you still have space for another fan tho. A 60mm exhaust mounted on the pci slot covers.

 

[bonehead123]

IMHO, because hot air naturally rises upwards, you could increase the air flow out of the case by using the 4 small ones as intakes and reverse the cpu fan so it is pushing the hot air up out of the case and away from the cpu core...

Also remember that the other components in the case need some airflow too....which the 2 small fans at the front should easily provide given the layout you have

 

[BonzaiDuck]

There's not going to be any appreciable "pressurization" of that case.
"Air flow" is what moves hot air out, not pressure.
Air flow is accomplished by a balance of intake and exhaust, while creating as little turbulence as possible.

Not sure if I "totally" agree. We've seen an improvement in cooling for heatpipes exhausting to the rear exhaust fan with Intake-CFM > Exhaust-CFM as far as cumulative fan rating. WGusler had removed the sidepanel to his setup, and found something like a 3C increase in CPU temperatures even if the RPM's of the CPU fan were the same.

On the turbulence, I suppose it would depend on the rig. I'm only guessing that turbulence means white-noise -- therefore more noise. My biggest problem with noise from air-turbulence arises at the exhaust port, because I always deploy a more powerful fan there that doesn't quite balance with the intake -- by design.

the main thing -- excluding this "pressurization" issue -- is to insure some sort of directed airflow over warm components. Barring that, the directed airflow would mostly go through any heatpipe coolers or radiators and exhausted immediately.

If I was making a point, it was that smaller case-interior volume is the next best thing to "ducted" and directed airflow over heat-generating points. Which follows your observation about good airflow. Truth be told, though, directed airflow is often accomplished by ducting, and ducting increases air pressure at key points by pushing air through a narrow aperture and passing it over the hot component. So leaving the pressure issue alone, lower case volume (smaller case size) can accomplish this even without building "little ducts."

 

[aigomorla]

My question though is this..... Should all 4 of those side case fans be intake? Or should 1 of them be an exhaust? What would you do?

The two which are sitting next to the heatsink should be intakes... pulls air inside.
This way you can get rid of the fan which sits on top of your heat sink.

The two at the bottom can be exhaust, or have 3 intake, and 1 exhaust.


I would give that a try, and see if the thermals are kept in check.

 

[Blain]

Turbulence causes air flow to slow down, slower moving air means heated air is evacuated at a lower rate.
A negative by-product of air turbulence, in the PC world, is higher noise levels.
If the top fan and two rearward fans are both blowing in on the HS area, they are "fighting" one another = turbulence.

These issues need to be put to bed by thebigbolgna.
He should do a DOE (design of experiment), and determine for himself the optimal configuration of the fans he currently has installed.

 

[BonzaiDuck]

Turbulence causes air flow to slow down, slower moving air means heated air is evacuated at a lower rate.
A negative by-product of air turbulence, in the PC world, is higher noise levels.
If the top fan and two rearward fans are both blowing in on the HS area, they are "fighting" one another = turbulence.

These issues need to be put to bed by thebigbolgna.
He should do a DOE (design of experiment), and determine for himself the optimal configuration of the fans he currently has installed.

Sure -- I can buy that. But if the turbulence is mostly between the exhaust side of a heatpipe cooler and the rear exhaust port, not a factor.

I don't know how to characterize the airflow from my 200mm intake fans. But they help push air through my heatpipe cooler, while a 120mm fan pulls it out.

But here's an example of "fans fighting each other." You put a radiator at an intake with one or more fans. Then, you have more intakes adding to case pressure. This would inhibit airflow through that particular radiator.

What's good for one type of cooler or heat-exchanger placement, might be bad for something different.

 

[jacktesterson]

Turbulence causes air flow to slow down, slower moving air means heated air is evacuated at a lower rate.
A negative by-product of air turbulence, in the PC world, is higher noise levels.
If the top fan and two rearward fans are both blowing in on the HS area, they are "fighting" one another = turbulence.

These issues need to be put to bed by thebigbolgna.
He should do a DOE (design of experiment), and determine for himself the optimal configuration of the fans he currently has installed.

I agree

I may do this as I am taking 6 weeks off work in 2 weeks. I may do this.

To be honest my machine is quiet as is so I've left it alone since posting, but was curious if I should change it. (all 4 are still intake, HS fan is still downwards)

Would the 80mm fan on the PSU act as an exhaust somewhat?

 

[ClockHound]

While it would be interesting to see the results of the tests, it seems you have already achieved the goals of quiet operation with stable temps.

Yes, the 80mm in the PSU is acting as an exhaust, so there's that. Plus the case is small enough that it is positively pressurized sufficiently so hot air is flowing out through the cracks. If there were dead spots in critical areas, it would be reflected in higher temps and noise.

No matter, with your level of positive pressure all negativity is being pushed out of the case anyways. Next up, positively pressurizing this thread. ;-)

 

[greenhawk]

I doubt you'd gain anything from switching them to exhaust. If air needs to get out, it gets out. Plus, you can never have a too large supply of cool air.

Only issue with all the fans blowing in is an increase in noise as the hot air is not leaving fast enough.


OP, Given the power supply is probably sucking air out, I would just reverse the CPU fan to blow out and leave the 4 side fans blowing in.

Having fans next to each other blowing in different directions can start a little loop of air which does not help with cooling at all.