Even before the first Pentium era of the early 1990s, PC CPUs were already powerful enough to require meaningful and capable cooling setups to keep their temperatures in check. Although there were configurations that could make it by with passive cooling, most PCs were already relying on active cooling solutions. Not many years later, active cooling not only became a de facto requirement, but the high thermal loads generated by processors required that heatsinks have powerful and noisy fans. The pushback from this increasingly noisy era of computing, in turn, effectively spurred the modern market for high-end passive coolers for use in low-noise (but still high-performance) PCs.

The history of passive coolers for high-performance PCs is not very rich – the physics of heatsinks is a well understood field – but, occasionally, we would see some companies make a valiant effort to produce a passive cooler that would be viable on the open market. There were even instances where manufacturers tried to make the entire PC passively cooled, as Zalman’s effort 20 years ago with the hefty TTN-500AF case. Nevertheless, no solution was long-lived, mainly because the ever-rising power (and cooling) requirements would quickly overwhelm the capabilities of the passive coolers of the time.

But now in 2022, perhaps the world is ready for a change? To answer that question, in today’s review we are having a look at the NH-P1, a surprising passive CPU cooler released by one of the most reputable active PC cooler manufacturers, Noctua.

Having already established their name (and then some) with low-noise active coolers, Noctua has turned their attention to the final frontier of low-noise cooling: passive CPU coolers. And in order to accomplish this, Noctua has built a pure heatsink. A very, very large pure heatsink that's suitable for CPUs.

Throughout all of their history, Noctua has never made a purely passive cooler before, which makes the NH-P1 a remarkable product from the company. The company has significant experience with cooling with their traditional actively cooled products, but suffice it to say, moving a lot of heat without the help of forced airflow is a much bigger challenge – and one we're eager to see a company like Noctua undertake. So is the NH-P1's sheer size alone capable of withstanding the intense thermal loads of modern processors? Let's find out.

Packaging & Bundle

The NH-P1 comes into a well-designed cardboard box, following the same simple artwork that Noctua is using for nearly all of their products. It is an elegant design, focused on delivering as much information as possible rather than relying on striking colors to catch the eye. The sheer size of the packaging hints that the NH-P1 is nothing alike any air cooler we have seen before. Inside the box, we found the cooler very well protected below layers upon layers of thick cardboard packaging. The supplied mounting hardware and extra items can be found in a smaller, compartmentalized cardboard box.

Aside from the typical mounting hardware necessary to mount the NH-P1 onto a CPU socket, Noctua also supplies a nice screwdriver, a tube of NT-H2 thermal grease, and a metallic case badge. And, while perhaps sacrilegious for what's meant to be a fully passive cooler, there are also two wire holders for installing a fan, should the user ever wish to do that.

The Noctua NH-P1 CPU Cooler

A simple glimpse on the Noctua NH-P1 is enough for anyone to realize that this is no run-of-the-mill CPU cooler. To begin with, the sheer proportions of the NH-P1 are massive beyond comparison. At 15.8cm x 15.4cm x 15.2cm (essentially a 6.5-inch cube), the NH-P1 dwarfs typical tower coolers – which are already pretty large – taking about three times the volume of a fully-assembled NH-U12S. And its 1.18kg weight makes it heavier than some laptop computers.

Considering both the size and the nature of the NH-P1, it is bound to face compatibility issues with both systems and cases, as well as limited compatibility with CPUs. To that end, Noctua provides detailed compatibility tables that include both system parts and PC cases, to help buyers get a better idea ahead of time over where the plus-sized passive cooler can fit.

Case compatibility aside, the NH-P1 supports nearly all modern CPU sockets, including Intel's LGA-11xx/1200 socket and latest LGA-1700 socket, as well as AMD’s socket AM4. Threadripper is left out in the cold, however, as it would not be possible for the NH-P1 to handle the extreme thermal requirements such a high-end processor.

Despite its massive proportions, the NH-P1 sports only thirteen fins. The fin spacing is nearly ten times that of a typical air cooler, and every single fin is perforated with 33 rectangular holes so as to optimize passive airflow. This configuration would make typical cooler fins too thin and flimsy, so Noctua greatly increased the thickness of each fin as well. Finally, the fins also are not pressed onto the heatpipes but soldered, ensuring the long-term mechanical strength of the cooler.

Six heatpipes are responsible for transferring the bulk of the thermal energy generated by the CPU onto the fins of the cooler. The heatpipes start from the base of the cooler, positioned exactly in parallel to each other, and extend to just one side of the base towards the top half of the fins in a symmetric fan pattern. They are made out of copper but are fully nickel-plated to prevent surface corrosion.

The base of the NH-P1 is almost typical for any modern heatpipe-based cooler, with the exception that six of the fins extend and are directly attached to the base itself. This is mostly to increase the mechanical strength of the NH-P1, as the colossal fin array could not be reliably supported by the heatpipes alone. Yet it may also be playing a little part in the thermal performance of the cooler as well by allowing a little bit of thermal energy to transfer directly from the base towards the fins.

The bottom half of the base is made out of nickel-plated copper, maximizing the heat transfer rate from the CPU to the heatpipes. It is extremely well machined, perfectly flat, and smooth. The rest of the base serves only as a mechanical support and is mostly made out of aluminum, with the exception of the mounting bracket that is nickel-plated steel.

Testing Methodology

Although the testing of a cooler appears to be a simple task, that could not be much further from the truth. Proper thermal testing cannot be performed with a cooler mounted on a single chip, for multiple reasons. Some of these reasons include the instability of the thermal load and the inability to fully control and or monitor it, as well as the inaccuracy of the chip-integrated sensors. It is also impossible to compare results taken on different chips, let alone entirely different systems, which is a great problem when testing computer coolers, as the hardware changes every several months. Finally, testing a cooler on a typical system prevents the tester from assessing the most vital characteristic of a cooler, its absolute thermal resistance.

The absolute thermal resistance defines the absolute performance of a heatsink by indicating the temperature rise per unit of power, in our case in degrees Celsius per Watt (°C/W). In layman's terms, if the thermal resistance of a heatsink is known, the user can assess the highest possible temperature rise of a chip over ambient by simply multiplying the maximum thermal design power (TDP) rating of the chip with it. Extracting the absolute thermal resistance of a cooler however is no simple task, as the load has to be perfectly even, steady and variable, as the thermal resistance also varies depending on the magnitude of the thermal load. Therefore, even if it would be possible to assess the thermal resistance of a cooler while it is mounted on a working chip, it would not suffice, as a large change of the thermal load can yield much different results.

Appropriate thermal testing requires the creation of a proper testing station and the use of laboratory-grade equipment. Therefore, we created a thermal testing platform with a fully controllable thermal energy source that may be used to test any kind of cooler, regardless of its design and or compatibility. The thermal cartridge inside the core of our testing station can have its power adjusted between 60 W and 340 W, in 2 W increments (and it never throttles). Furthermore, monitoring and logging of the testing process via software minimizes the possibility of human errors during testing. A multifunction data acquisition module (DAQ) is responsible for the automatic or the manual control of the testing equipment, the acquisition of the ambient and the in-core temperatures via PT100 sensors, the logging of the test results and the mathematical extraction of performance figures.

Finally, as noise measurements are a bit tricky, their measurement is being performed manually. Fans can have significant variations in speed from their rated values, thus their actual speed during the thermal testing is being recorded via a laser tachometer. The fans (and pumps, when applicable) are being powered via an adjustable, fanless desktop DC power supply and noise measurements are being taken 1 meter away from the cooler, in a straight line ahead from its fan engine. At this point we should also note that the Decibel scale is logarithmic, which means that roughly every 3 dB(A) the sound pressure doubles. Therefore, the difference of sound pressure between 30 dB(A) and 60 dB(A) is not "twice as much" but nearly a thousand times greater. The table below should help you cross-reference our test results with real-life situations.

The noise floor of our recording equipment is 30.2-30.4 dB(A), which represents a medium-sized room without any active noise sources. All of our acoustic testing takes place during night hours, minimizing the possibility of external disruptions.

*noise levels above this are not suggested for daily use

Testing Results

As the Noctua NH-P1 does not have a fan at all, for fairness’ sake, we are comparing its performance with other coolers running at their low-noise mode (half fan speed). Still, due to the nature of the NH-P1 or, more precisely, its colossal mass, we tripled our regular testing time, allowing the temperature to stabilize.

Meanwhile, we are not publishing any noise-related tests for the obvious reasons: the NH-P1 does not generate the least bit of noise under any circumstances (at least, not while an optional fan is not attached to it). So all we could measure is the ambient noise, which is a function of our test environment rather than the cooler itself. (Though we were tempted to throw it into an anechoic chamber just to produce some truly crazy figures)

Finally, we should note that we are testing the NH-P1 in its purely passive form, without any forced airflow at or even near it.

As expected, the Noctua NH-P1 cannot compete directly against most typical CPU coolers that make use of forced convection. To that end, the NH-P1 displayed an average thermal resistance of 0.4064 °C/W, which is very high if compared against a top-tier CPU cooler, but does land in the same league as basic stock CPU cooler designs.

The Noctua NH-P1 can handle loads lower than 100 Watts rather well. The temperatures will be high, but modern processors should happily operate at temperatures up to 50°C above ambient – assuming that the internal temperature of the PC case is relatively close to that of a typical household room (~22°C). Prolonged loads greater than 120-140 Watts will have the temperature delta widening too far for the NH-P1 to keep a chip from thermally throttling. The good news is that modern CPUs are designed to handle just such a thing (see: virtually any compact laptop in the last decade), but our testing equipment is another story: we had to stop our testing after 200W in order to avoid damaging our equipment.

We should point out again that these results require excessively prolonged testing time than normal, as the thermal inertia of the NH-P1 is outworldish. For typical PCs, where the CPU is not constantly running at full load, the thermal performance of the NH-P1 is bound to seem much better. Still, we would not recommend using it on infamously hot processors and/or on an overclocked processor. Think something closer to AMD & Intel's standard 65W parts, rather than their extreme K/X parts.

Final Words & Conclusion

Noctua is one of the most reputable PC cooling manufacturers for a reason: their products typically are well-designed and of excellent quality. The NH-P1 is no exception to that rule, and the timing of its release definitely is not coincidental. For example, with AIO coolers becoming increasingly popular over the past few years, typical PC cases nowadays are a bit wider and roomier, which allowed for the NH-P1 to greatly lengthen its compatibility table, as it would not fit the width of many older case designs.

Using a passive CPU cooler does have disadvantages, the most important being the (relatively) low thermal performance. The Noctua NH-P1 overcomes that issue, with the cooler offering passable thermal performance for most modern desktop PC processors. Its steady-state thermal resistance is comparable to that of a basic stock CPU cooler but its thermal inertia is colossal, meaning that it can maintain good operating temperatures under typical operational circumstances, as the processor will only be facing near-maximum loads for short periods of time.  This massive thermal inertia comes from the respectively huge mass of the NH-P1, which limits the compatibility of the cooler and greatly increases its manufacturing cost.

With that said, the use of a passive CPU cooler also has other implications that need to be considered. The two major implications are significantly higher internal system temperatures and lack of airflow for improved VRM/motherboard cooling. Even in a well-designed passive system, the temperature of the motherboard’s critical components is almost certainly going to be significantly higher than a typical PC. Significant forced ventilation could remedy that, but the use of multiple case fans would defeat the purpose of a passive CPU cooler to begin with. Therefore, even if the CPU cooler itself could handle greater thermal loads, it would be problematic for the rest of the system to have such a huge dissipation of thermal energy inside it without any significant means of removing it.

It is also possible to add an optional 120 mm fan on the Noctua NH-P1. Most would think that using a fan defeats the purpose of having a passive CPU cooler in the first place but, on the other hand, most modern motherboards allow for the programming of meticulous cooling profiles. It would be very realistic to have a top-tier CPU and have the cooling fan operate only when, say, the temperature rises above 80 °C, even if as just a backup.

In terms of quality, Noctua never disappoints. If anything, their products usually are the benchmark for how top-tier designers and manufacturers should practice their business. The NH-P1 is very well-designed mechanically, excellently assembled, and is built from premium materials, all as we'd expect from a high-end Noctua product. But designing and building such a premium product is costly, and that is reflected by the $110 price tag of the NH-P1. The sheer mass of the NH-P1 ends up being a major factor here, as the costs of the nearly half a kilo of additional machined copper and aluminum needed to build such a large heatsink add up quickly.

Ultimately, it is clear that Noctua does not have the mainstream market in mind, but rather is going after advanced users who understand and accept the implications of using a passive cooler. In that respect the NH-P1 is very much a niche product, but it's also a product that fills that niche well. Building quiet PC systems has always been a popular design choice, and to that end Noctua's NH-P1 should find itself right at home in the silent PC community.