Noctua NF-A14x25 G2 PWM: Finally a first-class 140mm fan

Details of the Noctua NF-A14x25 G2 PWM

The range of 140mm fans is now expanded by the Noctua NF-A14x25 G2 PWM. The wait for this model was very long, but finally, after various hardships, everything was brought to a successful end. This, by the way, is also indicated by our in-depth tests, from which the NF-A14x25 G2 fan takes away the “best” results across many usage scenarios. This is also due to the significant innovations in the aerodynamic design.

So, after the circular frame model (NF-A14x25r G2 PWM), the NF-A14x25 G2 PWM fan is becoming a reality on the retail market. Their frame is already square, with the standard spacing of mounting holes for 140 mm fans. This is the main thing that distinguishes the models with and without the “r” (in the fan designation) from each other.

While the NF-A14x25r G2 PWM’s usage options are quite limited (and primarily they are fans for the Noctua NH-D15 G2 cooler), the NF-A14x25 G2 PWM with its square frame already has a “standard” mounting, which makes it possible to use them in all positions that are designed for 140mm fans. The mounting hole spacing of the NF-A14x25 G2 PWM is already 125 mm (instead of the 105 mm of the NF-A14x25r G2 PWM).

The aerodynamic foundation lies in the 9-bladed impeller. The individual blades have distinctly curved leading edges and yet they also have an unconventional central bend that makes them look “humped”. This is in order to achieve a greater pressure differential at the front, closer to the impeller, than with traditional designs.

To increase the efficiency of the area around the inner cross-section, the outer casing of the impeller hub also has a specific modification (Centrifugal Turbulator). It has protruding grooves in the shape of triangular arrows. Simply put, these are designed to better eject the incoming airflow at the center of the fan in front of the fan, which is supposed to contribute to higher pressure around the impeller hub. In other words, these areas should achieve higher airflow than in fans with a smooth impeller hub surface. The benefit of these elements is difficult to quantify, and even Noctua talks about the need for an appropriate symbiosis. There are more of these micro-optimisations and although they cannot be expected to have a significant impact, they certainly have some contribution to the overall good result.

When looking at the entire impeller area, the size of the gaps between the blades should also be noted. For example, compared to the 140mm BeQuiet! Silent Wings Pro 4, which has two fewer blades, these Noctua NF-A14x25 G2 PWM fan blade gaps are smaller, but also larger than those of the Thermaltake Toughfan 14 Pro.

Although it cannot be generalized that smaller gaps are better (the overall aerodynamic design plays a big part in this), they also help determine the static pressure and the airflow that will be achieved through a particular obstacle. Fans with larger gaps may be less able to withstand back pressure and thus will achieve lower airflow through obstacles. But again, this is difficult to compare because, for example, at the same speeds, in this discipline, a “slightly weaker fan” may in turn be significantly quieter and produce more attractive results at comparable noise levels. It may or may not be the case. It depends on the interplay of the individual elements of the fan, i.e. how well a particular design is optimized with respect to its entire aerodynamic structure.

The rotor is made of Liquid Crystal Polymer (LCP) and the strength of the blades is high even at the tips. This is also due to the use of extra thickness up to approximately 3 mm.

The aerodynamic micro-optimisations of the NF-A14x25 G2 PWM fan also include the traditional channels on the trailing edges. In their context, Noctua writes about air acceleration. This is in the sense that these channels suppress intake microturbulence by a certain degree of laminarization, which is supposed to result in higher airflow at lower noise (less turbulent flow is quieter flow here). New (compared to the older generation) are the winglets at the very tips of the blades, very close to the inner tunnel of the frame.

The gap between the blades and the frame is very small here, only about 0.7 mm. This design (tight) primarily increases the static pressure, which has a positive effect on the drop in airflow through an obstacle – this (drop) will be lower than if this offset of the impeller tips from the tunnel were larger. However, this adjustment is not of particular importance either. Sure, it contributes to excellent results, but expect only reasonably low gains from it. However, it’s obvious that Noctua really cares about perfecting the void space between the blades and the frame.

The intentions of maximizing the static pressure that shapes the blade-frame relationship are also evidenced by the surface treatment of the inner part of the tunnel with the pyramidal formations – Inner Surface Microstructures. These are embedded in the frame and their role is to create a small turbulent layer to better resist back pressure and thus a decrease in airflow due to the resistance of an obstacle. The depth of these formations is relatively small, less than in the NF-A14 PWM fans, because its depth depends on the gap between the fan blades and the fan tunnel. And that, as you already know, is very small. And the smaller the gap, the smaller/smoother the ISMs can be for optimal results.

Then on the intake side of the frame, what’s also not missing are the steps (Stepped Inlet Design) to suppress tonal peaks resulting from the intake of air streams. These are also quite small and their design is tailored to the needs of the specific fan.

From the rear, a full-circuit sealing gasket is pre-installed, which is new. Unlike “ordinary” anti-vibration pads (as they used to be on older fans and as they still are on the front of this model – NF-A14x25 G2 PWM), this solution eliminates the height differences between the corners and other parts of the frame. Anyway, don’t imagine that the fan will fit perfectly to the radiator and there will be no gap between the fan frame and the radiator frame. There will be, but significantly smaller.

The size of the gap between the anti-vibration seal and a radiator frame is well illustrated in the photo below. There is still some gap, but it is smaller than it would be with traditional anti-vibration pads.

The small protrusions around the mounting holes also create a certain offset from a radiator or other obstacle. These were not present on older pads, and are also present here to relieve mounting pressure that may have caused deformation of the frame that could result in unwanted collision with the blades.

You may have also read about the complications with frame warping under certain circumstances in prototype stage fans in our interview with Noctua. One of the last modifications to these fans was to reinforce the corners with additional braces in the frame. Its material composition combines ABS and PBT.

It should be added from the basic information that the NF-A14x25 G2 PWM fan reaches speeds up to 1500 rpm, the slower LS-PWM variant (NF-A14x25 G2 LS-PWM) is then up to 800 rpm.

And one more thing: To navigate through the result graphs as easily as possible, you can sort the bars according to different criteria (via the button on the bottom left). By (non)presence of lighting, profile thickness, brand, bearings, price or value (with the option to change the sorting to descending or ascending). In the default settings, there is a preset “format” criterion that separates 120mm fans from 140mm fans.

• Contents
• Details of the Noctua NF-A14x25 G2 PWM
• Overview of manufacturer specifications
• Basis of the methodology, the wind tunnel
• Mounting and vibration measurement
• Initial warm-up and speed recording
• Base 6 equal noise levels…
• ... and sound color (frequency characteristic)
• Measurement of static pressure…
• … and of airflow
• Everything changes with obstacles
• How we measure power draw and motor power
• Measuring the intensity (and power draw) of lighting
• Results: Speed
• Results: Airlow w/o obstacles
• Results: Airflow through a nylon filter
• Results: Airflow through a plastic filter
• Results: Airflow through a hexagonal grille
• Results: Airflow through a thinner radiator
• Results: Airflow through a thicker radiator
• Results: Static pressure w/o obstacles
• Results: Static pressure through a nylon filter
• Results: Static pressure through a plastic filter
• Results: Static pressure through a hexagonal grille
• Results: Static pressure through a thinner radiator
• Results: Static pressure through a thicker radiator
• Results: Static pressure, efficiency depending on orientation
• Reality vs. specifications
• Results: Frequency response of sound w/o obstacles
• Results: Frequency response of sound with a dust filter
• Results: Frequency response of sound with a hexagonal grille
• Results: Frequency response of sound with a radiator
• Results: Vibration, in total (3D vector length)
• Results: Vibration, X-axis
• Results: Vibration, Y-axis
• Results: Vibration, Z-axis
• Results: Power draw (and motor power)
• Results: Cooling performance per watt, airflow
• Results: Cooling performance per watt, static pressure
• Airflow per euro
• Static pressure per euro
• Results: Lighting – LED luminance and power draw
• Results: LED to motor power draw ratio
• Evaluation