Case temps puzzle

[Yardstick]

I have a classic Coolermaster ATCS 210 (the one with the clear blue door). For my requirements it still does a great job and I will continue to use it for as long as it is practical to do so. However, during an idle moment last weekend I though I would try and improve the airflow through the case. The ATCS 210 has two 80mm fans (both blowing out), one at the rear of the case, the other a blowhole. In addition, I have a top mounted PSU with a 120mm fan drawing air from inside the case and venting out the back.

So following the theory that the airflow would increase inside the case, I reverse the rear 80mm fan and sure enough the throughput of the top fan appeared to increase. However, 30 minutes into a gaming session I noticed a case temp of 30 C - ambient room temp was 20 C. 30 C was much higher than I'm used to with this case even at the height of summer, so I reversed back the rear fan and after another 30 mins under load the case never rose above 24 C.

Must say this confused me - why would two exit fans outperform one input / one exit fan so comprehensively?

 

[misterPK]

When you had two fans blowing out, you had air being drawn in through other vents and gaps in your case. Then when you changed it, you halved the extracting flow and increased the inwards flow. This means there's a lot more air sitting around inside your case to get hot.

PK!

 

[WILD9]

As above, you probably created a bit of an air circuit directly between the fans so cold air was drawn in one and then sucked out the other while the warm air below was left to convect up and out.

 

[EsaT]

Not much ways for improving airflow unless case has restricting square mesh in front of back exhaust fan.