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Hydro H70 push/pull fan CFM question

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April 12, 2011 4:20:54 AM

When I installed I didn't want to take out the adjustable fan that came with my case, so I just left it on high as the pull fan and used one of the included with the H7 as a push. I just found out they have different CFM ratings, and it has been running at 61.2 Push/79 Pull.

I haven't noticed any issue with it, but can I leave it like this or will it affect performance or damage something?
a b K Overclocking
April 12, 2011 9:33:43 AM

Because the density of the H70 rad, you should be looking more into the static pressure the fans can create rather than the CFM. A fan that can create a higher static pressure will be able to push more air into the thin gaps of the radiator. Ideally, you should have 2 of the same fans, but I don't think you'll break anything.
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April 12, 2011 9:58:27 AM

gracefully said:
Because the density of the H70 rad, you should be looking more into the static pressure the fans can create rather than the CFM. A fan that can create a higher static pressure will be able to push more air into the thin gaps of the radiator. Ideally, you should have 2 of the same fans, but I don't think you'll break anything.

They are both 2000 RPM fans. The case one has 2 lower modes, whereas the H70's only has one, but I have auto-control disabled anyway, so its always running at 2k.
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a b K Overclocking
April 12, 2011 10:56:57 AM

That's RPM. I was talking about static pressure.

Nevertheless, I still think you won't break anything.
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April 12, 2011 11:54:29 AM

gracefully said:
That's RPM. I was talking about static pressure.

Nevertheless, I still think you won't break anything.

How do I check the static pressure.. I thought it was based mainly on RPM?
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a c 324 K Overclocking
April 12, 2011 1:15:32 PM

This won't damage anything, but you will likely achieve lower than the slower fan in terms of actual performance. No fan can achieve the actual 'advertised' CFM rate unless it is in a mount, without a grille and not pushing against a radiator. Factor in the resistance of anything other than just air, and it will be lower.

Static pressure can be compared to the actual power of the fan. Sure CFM is good, but static pressure is how much power it continues to have as it pushes the air when resistance is present...the ability to push that column of air vs. the actual amount of air moved in a perfectly non-restrictive environment.

BTW...this should probably be moved to the watercooling forum...there are some folks over there that actually are using these and more watercooling principles apply to these coolers than air cooling.
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a b K Overclocking
April 12, 2011 3:07:03 PM

Yes, CFM measurements are usually quoted in "perfect", zero-resistance environments. You'll probably only get half of that with grilles, and probably an eighth or so with a rad.

A fan that has a high CFM doesn't necessarily have a high static pressure, which is more important with rads which only have very tiny slits for the air to pass through.

In any case, I still think you won't break anything. ;) 
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a c 324 K Overclocking
April 12, 2011 3:57:30 PM

^Yes...that's one of the fan test links I was looking for...I need to add this to the sticky. Sweet find...we're missing some good fan links.

Got any more? PM me if so.
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April 12, 2011 7:29:38 PM

Best answer selected by Nakkiel.
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