Building a small form factor PC: An exercise in planning.

23 August 2026

A while ago, I built a new computer. It wasn't my first computer, nor would it be my last. But it's the one I use by far the most.

I had previously spent a large amount of money on building what was, at the time, a 'no compromises, top of the line' computer - I'm talking AMD 7950X3D, RTX 4080ti, the works. And all in a massive, white, Hyte Y70 case.

And it was beautiful.

However, with time, I came to realise two things - I really didn't need all that horsepower, and it was MASSIVE. As such, I began to research the other end of the PC building spectrum. The world of small form factor (SFF) computers. It piqued my interest, that there were these highly performant, quiet, mature looking computers that could still do everything I wanted. I'm never sure if I am in the minority when I think the average 'gaming PC', with its excessive LEDs and edgy aesthetic, are rather tough on the eyes.

As I read further, it became increasingly clear that I NEEDED to try one for myself - it seemed like the solution to all of my woes. But, with every positive thread online about these machines, was someone having a bad experience of overheating, loud machines, and lost performance. I have always felt that there is beauty in the balance between extremes, so I had no doubt I could make it work.

At a simple level, a computer will only overheat if the peak cooling capacity is less than the peak thermal output. However, you must also consider that it's not 'the computer' that overheats, but a single component of that computer - usually the CPU or GPU, more rarely the power supply or drives. It doesn't matter how many fans your computer has, if you cant first transfer that heat from the components into the air. And if the case is small, there is very little air in the case to transfer heat to - you can see easily you could start going in circles trying to solve the issue. It's best to select one 'holy grail' part to build around, and go from there.

As such, I started with a case, and configured my PC around that. I picked the 'Fractal Design Terra' in green. A truly beautiful little PC case, albeit for a somewhat inflated price. Next, was a carefully selected CPU. AMD was still leagues beyond Intel in terms of heat & power to performance ratios, so I went with the 'AMD Ryzen 7 9700X'. It's unique in being the only AMD CPU of the past few generations to have a 65W maximum TDP. Thermal Design Power (TDP) measures the maximum amount of heat in watts that a cooling system must dissipate during normal, non-boosted base operation. Most CPUS are 120w or more. Less power means less heat, meaning less required cooling. Simple. Now, I should just grab any old cooler and-

Wait. Hold on now. This is a SFF PC, it's not that simple. We have very little space for a CPU cooler. In fact, the Fractal Terra has. Wait. What? Between 48 mm and 77 mm? How does that work? You see, the 'spine' of this case, where you mount your components, can be moved from side to side. This allows you to get more clearance if you have a particularly large part, such as the GPU. So, lets pick a GPU first, then come back to the CPU cooler.

I'm going for Linux full time, so Nvidia is simply not an option. So, what's the fastest AMD GPU right now? Turns out it was the RX 9700 XT. Now, like all GPUs, the basic design is licensed out to a load of other companies to sell their own versions with different cooling solutions, dimensions, etc. The lovely online community has already created a massive spreadsheet of all these versions and their dimensions, so I simply selected the one with the shortest width. That was the 'PowerColor Reaper Radeon RX 9070 XT' at 41mm.

The interior width of the Terra is exactly 120mm. 41mm is given to the GPU, leaving 79mm to play with. So, 79mm of CPU cooling right? Nope! The Terra is annoying in that, if any fan is too close to the vented walls, it makes a loud sound caused by air turbulence. So, lets subtract 10mm per side for 'buffer zones'. That leaves us with 59mm of space. And of course, the cooler isn't exactly flush, the motherboard has to first be mounted, and it sits on top of that. Lets call it 53mm to be extra safe. Not that motherboards are that thick.

Welp, this all makes for a very small CPU cooler, so it's got to be amongst the best in its class. Water cooling is far too bulky, so it's purely air cooling for us. As such, I landed upon the 'Thermalright AXP90-X47 FULL CPU Cooler'. As you may guess, it is 47mm tall (including fan), so within our size requirements. I selected this one specifically because the 'FULL' in its name alludes to its full copper construction. The superior thermal conductivity of copper compared to it's more common aluminium-finned counterparts should ensure the cooling can't be topped. To be safe, I swapped out the fan for a 'Noctua A9x14 HS-PWM chromax.Black.swap 33.84 CFM 92 mm Fan'. Noctua are expensive, but they are undeniably the best fan makers around. Quiet, slim enough for the case, but pushes enough air to get by.

I also selected a larger 'Noctua A12x15 PWM chromax.black.swap 55.44 CFM 120 Fan' for the case fan. These Noctua fans CFMs (Cubic Feet per Minute) of air moved isn't actually exceptional, but they are reliable and some of the quietest. I also put a fan grill on it so no cables would accidentally stop it from spinning. Lord knows that's the last thing I need.

Nice! With the problematic parts selected and theoretically positioned, I can pick the other parts. They wont be seen, so simple, safe options will do here. A classic Corsair PSU, any old Mini ITX motherboard, drives-a-plenty, the best thermal compound money can buy, and cheap but high speed RAM. Because I built this before RAM prices went crazy. Lucky me. Here's the full parts list:

  • CPU:
    • AMD Ryzen 7 9700X 3.8 GHz 8-Core Processor
  • CPU Cooler:
    • Thermalright AXP90-X47 42.58 CFM CPU Cooler
  • Thermal Compound:
    • Noctua NT-H2 3.5 g Thermal Paste
  • Motherboard:
    • Asus ROG STRIX B650E-I GAMING WIFI Mini ITX AM5 Motherboard
  • Memory:
    • Corsair Vengeance 64 GB (2 x 32 GB) DDR5-6400 CL32 Memory
  • Storage:
    • Western Digital WD_Black SN850X 1 TB M.2-2280 PCIe 4.0 X4 NVME Solid State Drive
    • Western Digital WD_Black SN850X 4 TB M.2-2280 PCIe 4.0 X4 NVME Solid State Drive
  • Video Card:
    • PowerColor Reaper Radeon RX 9070 XT 16 GB Video Card
  • Case:
    • Fractal Design Terra Mini ITX Desktop Case
  • Power Supply:
    • Corsair SF750 (2024) 750 W 80+ Platinum Certified Fully Modular SFX Power Supply
  • CPU Fan:
    • Noctua A9x14 HS-PWM chromax.Black.swap 33.84 CFM 92 mm Fan
  • Case Fan:
    • Noctua A12x15 PWM chromax.black.swap 55.44 CFM 120 mm Fan
    • Nivithi 120mm Fan Grill

One quick assembly later and were done! Mostly. This is an SFF build damn it, show some respect. I want it to run cool and quiet, and usually you can have one or the other. But with some BIOS tweaks, we can mostly have both. First, I set the fan curves to 'quiet'. Then, I took time to undervolt the CPU.

Undervolt? Don't you mean overclock?

How primitive. Not at all. Whilst overclocking is the act of making a computer part run at a higher clock speed than its factory settings, undervolting is the process of lowering the electrical voltage supplied to your computer's CPU or GPU. Overclocking gives more performance at the cost of more power and thus higher temperatures, wheres undervolting uses less power and thus provides a lower maximum temperature, whilst losing no performance - you could even gain some! Here's some little temperature stats:

  • CPU Temperature While Idle:
    • 45.0° C
  • CPU Temperature Under Load:
    • 78.0° C
  • GPU Temperature While Idle:
    • 55.0° C
  • GPU Temperature Under Load:
    • 68.0° C

With a bit of fine tuning, I got it all working silent and happy. It goes to show what a good bit of planning and research can bring you, if you just take the time to try.

I have been using this PC for over a year now. It's performed admirably, has never given me an issue, and has never made me wish for something else. It has given me the confidence to build a compact NAS as well, which I may cover in a different blog post. And of course, it's damn small doing it.

That's a win in my books.