Radiator Push vs. Pull vs. Shroud Testing V2

Posted: January 15, 2012 in Radiators, Uncategorized
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TEST 1 No Shroud 125W Full Speed GT15 PULL

I figured for starters, I will test with the fan in pull at full speed as my baseline measurement with the expectation that shrouding will be better.

I got roughly 10.5C with a 53% efficiency or a 119C watt result at a 10C delta.  That is a bit lower result than my previous test bench, but that is to be expected since I am now insulating the lines and reservoir so very little heat is lost external to the radiator.

TEST 2 TFC 30mm Shroud 125W Full Speed GT15

Continuing with the fan in pull condition, I quickly placed the shroud under the fan and carried on with the same test:

While previous tests with the conventional 7 blade fan and slightly smaller RS120 radiator provided really good shroud gains, I’m measuring practically nothing with the GT15.  My only explanation is the lack of turbulence by the GT fan blades, since there is virtually no fan chop noise, it’s just not getting much of any benefit from the shroud (Less than .1C).  I’m a bit surprised by this, but it appears to be correct.  I’ll try again with the 25mm gutted fan as the shroud next.

TEST 3 Gutted 25mm Fan Shroud 125W Full Speed GT15

And while the TFC shroud is much nicer looking, most long term computer users end up with some sort of old fan collection in time and what better way to recycle than to snip off the motor and use the old fan housing as a shroud.  I did exactly that and sanded down the stubs flush for a nice cheap recycled 25mm shroud.

That did a hair bit better than 30mm, but still not really enough that I would be bothering with it.


The GT-15s are different than most fans, different in sound and apparently different in shroud benefits as well.

I really could not measure much of any gain in a pull scenario with the fans at full speed.  I measured less than .5C gains with both shroud tests while in pull using an MCR120 and the GT15s at full speed with an average 10C water delta.  In the end, I’m a bit surprised there is so little gains with GTs, but that’s what I’m getting so far.  Of coarse the higher the water delta the more gain you would get, but in a pull scenario I’m just not seeing much.

Regarding air flow CFM numbers, I really didn’t see any notable change. The anemometer pretty much bounced around a bit but hovered mostly in the 400 feet per minute range which equals about 43CFM using the port area as an assumed perfect conversion.  The actual amount of air moving through the radiator remained much the same regardless of shrouding…no air flow change.

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  1. Badelhas says:

    Hello Martin, great work, great site, congrats!
    Did you get to test push-pull on a 120mm thick 38mm rad? Linus and Tim Logan assure us it does help to reduce temps.

    • Martinm210 says:

      No, it could but considering I got gains on the RS120 slim/low density and none at all on the mcr120qp slim/low density, I don’t think you can assume any generalities. Likely depends on the exact radiator brand/type and perhaps the fan type too as it could adjust restriction enough to shift the curve to a hump in the fan curve etc. Very specific results is what I found so I would shy away from assuming more.

  2. Gadgety says:

    Very thoroughly done, Martin. I’m really glad you’re back to testing! I’m new to watercooling and I remember reading your previous conclusions about fan shrouds as I searched the net- I was set on getting shrouds. I appreciate this update.

  3. Dan says:

    Doesn’t it make sense that you see better results using a shroud on the XSPC than on the MCR since the FPI is very low on the XSPC at “sub 8 fpi” vs 20 fpi for the MCR?

    I would think that with the denser fin configuration; the further away you move the fan the harder it will be to penetrate the dense fin structure. Which would minimize befits obtained from decreasing the deadspot of the fans center.

    But on the less dense radiator you can realize the benefits more-so from decreasing the deadpsot since the loss of penetration into the fin structure is lessened.

    I would like to see how a 10mm shroud performs ? I guess is that you would have better performance.

  4. Sebastien says:

    hi martin thanks for another gret review with real numbers and real thoughts behind this.
    I have a question about push pull: you allways do the push pull tests with the sames fans and speed conditions, for both push and pull fan.
    I have a loop with 3 noctua nf p12 pushing fans and i have scythe karma low noise fans but low rpm too (500 rpm) that i don’t use becasue they are not enough powerfull by themselves.
    i was wondering if i add the scythe fans in pull with my noctua in push, do you think i should ahve some gain nor not at all or so ridiculous that it’s not worth installing it ???

    and my radiator is a swiftech mcr320 QP as you showed that radiator is important also.

  5. Ash says:

    I would assume there is more of a sound benefit than a cooling benefit when it comes to a shroud.
    as you dont have blades rushing within a few mm of radiator fins.

  6. Hydrow says:

    I have an idea but I don’t have the know age or equipment to test.

    I was wondering what the delta would be in a push pull setup on a 240mm radiator using 4x 120 SP vs 2x 120 SP push fans and 2x 140 mm A pull fans.

    Thank you

    • Martinm210 says:

      Not sure and no longer have the time to test either. Generally push plus pull or two pumps in series provides about a 30% flow gain. If you had an average 10c water to air delta, that would equal about 3C. Of coarse the delta is the bigger unknown. I have built high performance water systems than run no more than 2-3 degree deltas. I have also seen AIO kits push 20C. The gain is flow so degree gain is proportional to the unknown delta.

  7. Guy Cotnoir says:

    So no shroud will require less electricity to reach the same rpm as with shroud……interesting!
    I’d love to see if this results in higher or lower air flow with/without shround given the same rpm.