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Do you need an exhaust fan when you have a push/pull HSF?

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October 18, 2012 5:21:56 PM

I have an NZXT Phantom case with a Hyper 212 EVO HSF with two 120mm fans setup in a push/pull configuration. 2 inches away I have another 120mm fan acting as an exhaust fan. My question is do I really need that exhaust fan since the push/pull fans are pointed right at the exhaust opening and I can't imagine 2 inches would make a difference? Could I just remove the exhaust fan and let the push/pull fans blow right out that opening?

I am trying to create a positive pressure case as I live in Phoenix where is is VERY dusty. I already have two 200mm top mounted exhaust fans, so not sure I need that 3rd 120mm exhaust fan right by the HSF. Plus the push/pull fans are better and more powerful fans that push more air than the one I have on the exhaust and I am worried that the exhaust fan could be a bottleneck in the airflow.

Thoughts?
a b K Overclocking
October 18, 2012 5:42:34 PM

Well, the heat leaving the heatsink fans is going to rise rapidly, that is why it is desirable to have an exhaust for it, ideally on the top of the case, but the rear fan will also work to pull that way from the heatsink. You can certainly try without the exhaust but that may result in the heat simply condensing around your heatsink which is not desirable either. I suppose if you had positive pressure and made sure that rear port was the only/primary exhaust, it would naturally push any heat left around the heatsink fan out. Play with the configuration and check your temps, if you can get acceptable temps with positive pressure then go for it.
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a b K Overclocking
October 19, 2012 4:56:48 AM

I am planning on switching my exhaust fan to a pull fan on my CM Evo. To test if this is better I will run Prime95 for half an hour. Also I will play BF3 for half an hour and compare the temps of the two fan positions.

Will moving the fan affect mobo temps? What is recommended temp zone for mobos.
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October 19, 2012 7:16:46 AM

Yes it will more important to had an exhaust fan than push pull configuration........

2 inch is small but air can scattered back to the case when it hit the mesh....
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a b K Overclocking
October 19, 2012 1:14:53 PM

My MOBO never gets over 40 degrees, but I also have a down-draft heat sink. Even if you have push-pull, it is not going to shoot it directly horizontal out the slot in the back of your case, you would need a pretty powerful fan to do that. The hot air is going to leave the fan and go up towards the ceiling of the case, some will be pushed out the hole but a lot will simply collect above the heat sink and get sucked back into your "push" fan. Can't hurt to try (well it can, but shouldn't), but I would leave the exhaust even if you want to add another fan to the heatsink.
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a b K Overclocking
October 19, 2012 3:02:15 PM

chugot9218 said:
My MOBO never gets over 40 degrees, but I also have a down-draft heat sink. Even if you have push-pull, it is not going to shoot it directly horizontal out the slot in the back of your case, you would need a pretty powerful fan to do that. The hot air is going to leave the fan and go up towards the ceiling of the case, some will be pushed out the hole but a lot will simply collect above the heat sink and get sucked back into your "push" fan. Can't hurt to try (well it can, but shouldn't), but I would leave the exhaust even if you want to add another fan to the heatsink.


Great point. I was thinking the same. The air being pulled out of the heatsink will not go directly out the case.
So, an exhaust fan is needed. If a case doesn't have much headspace for a top fan it'll need to keep an exhaust
fan in the rear.
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a b K Overclocking
October 19, 2012 3:05:46 PM

You could, I suppose, set up the fans to push the air back towards the inside of the case (opposite direction of the rear exhaust) if it brings it close enough to the top exhaust, then you could get away without a rear exhaust and the HSF would make that hole more of an intake.
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a b K Overclocking
October 19, 2012 4:55:26 PM

Getting back to the topic of gerr's question. I'm doubtful now. I doubt that removing the exhaust fan would prevent a bottleneck. Two 200mm top fans and a push/pull heatsink seems like the CPU must be cool as is. So removing the exhaust won't make a huge difference in CPU temps.

Based on what gerr has said. It sounds like there is only 2 exhaust fans at the top. I know nothing about the intakes. I hope there is a side intake. Can you specify?
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a b K Overclocking
October 19, 2012 6:33:12 PM

I would say if it is not clearing the air out from around the CPU that could raise your temps, if it is just constantly cycling the same hot air through through the heatsink it is going to raise temps overall. Is there any reason you want to change your configuration besides creating Positive Pressure? Are the temps going too high? I was thinking you could go buy 1 additional fan, set the push-pull config as I stated before (blowing towards the inside of the case), and set the rear port as an intake (blowing onto the push fan of the HS if set up in my configuration). Thus, you get an intake to help move you positive, and it will provide fresh air to the CPU cooler, which will then push the heatsink air towards the top exhausts of the case (which are more likely to be towards the middle of the top of the case as opposed to directly over the rear top of the case).
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October 21, 2012 8:01:30 PM

This is for a new build that I have not turned on yet, but it's a 2500K I5 that I plan on overclocking.

My HSF is in a push/pull config pointed towards the back of the case, basically right at the exhaust fan and there is a 2" gap between the HSF and the exhaust fan.

I have 3 120mm intake fans, one in the front and two on the side. I have 3 exhaust fans, a single 120mm fan at the back of the case and TWO 200mm fans at the top of the case.

To make this case a positive pressure case, I have a fan adjustment control in which I will put the exhaust fans on low and the intake fans on medium to high.

With my rear 120mm exhaust fan running on low and only 2" from the HSF which is pointed right at it, I was wondering if that exhaust fan might cause a bottleneck in airflow and/or if it's even needed?
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