Designing a small CPU cooler is a difficult task in this day and age. Height is the main issue as there is no universally accepted heatsink clearance limit for small form factor cases, not that SFF is a standard in itself either. Taller heatsinks offer better performance at the cost of compatibility, while smaller, less capable models have to employ higher fan speeds to make up the difference. Complicating matters is the popularity of Intel mini-ITX motherboards for LGA1155/1156, most of which are laid out with the PCI Express 16x slot very close to the CPU socket, making heatsink length and width an issue as well.
Noctua dipped their toe into the small cooler market with the NH-L12, a miniaturized version of the NH-C14. For its size, it delivered exceptional performance in both its two fan (93 mm tall) and one fan (66 mm tall) configurations. Unfortunately it suffers from the size issues we just mentioned, being too tall for smaller enclosures and having a large footprint causing PCI Express slot interference in many mini-ITX boards. Noctua's second entry, the NH-L9i, takes a very different approach, focusing on compatibility above all else.
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