Which AIO radiator size should I choose – 420, 360 or 240mm?

When it comes to deciding between 420 and 360mm, there is a bit more to it than just “bigger is better”: While the 120mm NF-A12x25 G2 fans used on the NL-LC1-24 and NL-LC1-36 top out at 22.5dB(A) individually, the NF-A14x25 G2 140mm fans used on the NL-LC1-42 can go up to 24.8dB(A), which gives it a bit more performance headroom.

In practice, this means that the NL-LC1-42 can surpass the cooling performance of the NL-LC1-36 at higher fan speeds where it can leverage the full power of its NF-A14x25 G2 fans. Due to the higher airflow levels and the turbulence caused by the radiator, this performance benefit comes at the expense of up to ~5dB(A) higher noise levels. On the flipside, the NL-LC1-36 provides slightly better results at low fan speeds. This is due to the fact that the 120mm NF-A12x25 G2 fans have a higher blade coverage ratio than the 140mm NF-A14x25 G2 fans, which makes them more efficient working against high backpressure at low RPM.

Another thing to keep in mind is that the thermal performance advantage of the NL-LC1-42 at full fan speed becomes more pronounced with higher heat-loads: While we have measured around 1.2°C lower temperatures at 200W, the lead grew all the way to 3.8°C at 300W. At the same time, the NL-LC1-36 and NL-LC1-42 remained neck-and-neck in noise-normalised tests at ~22dB(A), where even at 300W heat load, the advantage of the 420mm radiator remained small at only 0.5°C:

Therefore, the heat-load alone should not dictate your buying decision: Even at 300W, the NL-LC1-36 will hold its ground when compared at equal noise levels, but the higher the heat-load, the bigger the performance headroom that the NL-LC1-42 can achieve at full fan speeds (at the expense of higher noise levels).

In summary, the NL-LC1-36 will provide optimal results in most use cases, and it even has a slight edge over the larger NL-LC1-42 in performance-to-noise efficiency at low fan speeds. This means that if your goal is to go as quiet as possible, we recommend going with the NL-LC1-36. If, by contrast, you simply want the maximum possible performance headroom or achieve the highest possible cooling performance at the expense of slightly higher noise levels at 100% fan speed, go with the NL-LC1-42 – just make sure that your case can fit 420mm radiators!