Radiator Alphacool R27-S420 420mm 18 FPI for liquid cooling, 3x120mm fan mounts

The Alphacool R27-S420 is a 420 mm liquid cooling radiator with 18 fins per inch (FPI) designed for custom PC water-cooling loops. It supports three 120 mm fans on standard mounts and offers enhanced surface area for heat transfer from coolant to ambient air. The radiator is intended for installation in full-size towers or rack systems where space allows a 420 mm unit, enabling improved thermal management for high-performance CPUs and GPUs while helping maintain lower fan speeds and reduced noise during operation.

Advantages

The R27-S420 combines a high fin density with a 420 mm length to deliver efficient heat dissipation in compact mounting configurations. Compatibility with three 120 mm fans lets users select fans for a balance of airflow and noise. Solid build quality and standard mounting spacing make integration into existing water loops and cases straightforward. The 18 FPI fin density provides a compromise between static pressure requirements and surface area, suitable for a wide range of fan types and cooling scenarios.

Suitable for

• Custom PC water-cooling loops for gaming and workstation systems
• Cooling high-performance CPUs and GPUs in full-size cases or racks
• Systems where a 420 mm radiator fits front, top, or bottom mounts

Key specifications

• Radiator length: 420 mm
• Fan mounts: 3 × 120 mm
• Fin density: 18 FPI (fins per inch)
• Compatibility: standard 120 mm fan spacing and mounting holes
• Use: liquid cooling heat exchanger for PC cooling loops

How to use

Install the radiator in a location within your case that accommodates a 420 mm unit, aligning the three 120 mm fan mounts to the chosen airflow direction. Secure fans to the radiator using the case or radiator mounting holes and connect the coolant tubing to the loop according to your cooling system layout. Fill and bleed the loop following the coolant and pump manufacturer instructions, then verify there are no leaks and that fans operate at intended speeds for the required static pressure and airflow characteristics.

Recommendations

Select fans that match the radiator’s 18 FPI fin density—fans with moderate to high static pressure perform best. When installing in tight spaces, prioritize higher static pressure fans to overcome resistance through fins. Regularly inspect and clean the radiator fins to maintain airflow and thermal performance, and ensure secure fittings and proper coolant levels to prevent leaks and maintain long-term reliability.