Does HEAT Always Go UP Inside A PC Case

One of my most controversial tech videos was when I replaced a regular fan with a slim fan on the bottom of a case. Some viewers told me that a bottom fan was unnecessary.

“Heat naturally goes up! No fan needed, you stupid oaf!”

That was one of the politer comments. Does heat always go up inside a PC case?

Old School Case

When I built a new PC for my FreeNAS file server in 2015, I got the NZXT Source 210 ATX case for $50 US. It’s an old school case with limitations not found in many of today’s cases.

  • Limited air intake through the front panel.
  • No support for 240mm or 280mm AIO liquid coolers.
  • This case had two knockout holes for an external radiator. Linus Tech Tips made a video about a 2005 water cooling kit with an external radiator.
  • Has eight 3.5″ internal bays and three 5.25″ external bays.

If I was to get a replacement case that can hold eight hard drives today, I would have to spend $125 US to $250 US.

I like the Fractal Design Node 804 Micro-ATX cube case for $140 US. The case has separate compartments for the motherboard and the hard drives. My current and future motherboards for the file server are micro-ATX.

Old School Airflow

When I assembled the case, I had four different brands of 120mm and 140mm non-PWM fans. I installed two 120mm fans in front, a 120mm fan in back, and two 140mm fans on top. The airflow goes through the front fans, across the processor, and out the back and top fans.

A case like this had three dead zones that lack air circulation to remove trapped heat: the front top, the back middle, and the front bottom.

Front Top Dead Zone

If you have media drives installed in the 5.25″ external bays, you will have tapped heat in the front top of the case. That heat shouldn’t affect the performance of the CD/DVD/Blu-Ray media inside the drive. If your media drive does get random read errors from overheating, the rest of the case might be on fire.

If you have hard drives on 3.5″ to 5.25″ adapter brackets, you might want to add a triple fan cooler with 40mm fans. I had three triple fan coolers for the hard drives inside my 2006 Linux file server. Those 40mm fans were loud even at low speed when I had the file server tucked away in a far corner.

You can also install an eight-bay 2.5″ drive cage into a 5.25″ bay. The cage fans are for cooling hard drives by pulling air from the front through the back. Depending on the quality of the SSDs, the fans might be optional and can be disconnected to reduce the noise.

Since I had nothing installed in the 5.25″ bays, the extra cooling wasn’t needed.

Back Middle Dead Zone

If you have expansion cards installed, you will have trapped heat in the back middle of the case. There are two methods for removing trapped heat if it becomes a problem.

  • A VGA card cooler that exhaust trapped heat through the back of the expansion slot.
  • A fan mounted on the side panel to blow air on to the expansion cards.

Since I didn’t have any expansion cards installed, the extra cooling wasn’t needed.

Front Bottom Dead Zone

If you have 3.5″ hard drives installed in the front bottom, you will have trapped heat beneath the bottom hard drive. With limited air intake through the front panel, the front fans won’t keep all the hard drives cool. This case can mount a 120mm fan on the bottom to pull out and push up trapped heat to the 140mm fan on top.

When testing revealed that the two bottom hard drives were hotter than other drives, I added a bottom fan to reduce the temperatures.

Rebuilding The File Server in 2020

For the 2020 rebuild, I replaced all the fans, added two hard drives, and a SAS controller card. I did make a mistake when I replaced all the fans two years ago. I didn’t test whether I still needed the bottom fan. The Arctic 120mm and 140mm fans can push a lot of airflow through the case.

Without the the bottom fan running, the case was the same temperature as before. I technically don’t need the bottom fan anymore.

Unless I need a slim fan for another PC, I’m leaving the bottom fan where it is for now.

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