7 Best 420mm Radiators for Liquid Cooling in 2026: Find the Right Fit for Your Loop

A 420mm radiator gives a custom loop room for three 140mm fans, but its length is only the first fit check. Thickness, fittings, and fan clearance can determine whether a build goes together cleanly.

These seven Alphacool full-copper options range from slim and cross-flow designs to thick radiators for builds with more space. The guide below helps you narrow the choice before you buy.

Best 7 420mm Radiators for Liquid Cooling Picks for 2026

Space-Conscious Pick – Alphacool NexXxoS XT45 Full Copper 420mm

Among 420mm radiators for liquid cooling, the Alphacool XT45 is worth considering when a 45mm-thick radiator fits your build better than a thicker model. Its copper fins, channels, and chambers pair with multiple fitting positions for routing flexibility.

Best For: Builders seeking a 45mm-thick copper radiator with flexible port placement.

Pros:

• Copper fins, channels, and chambers.
• Three fitting positions per inlet and outlet.
• Includes five plugs and two sets of mounting screws.

Cons:

• At 18.43 inches long, it still requires a case that accommodates a 420mm radiator.
• One-year manufacturer warranty.

The XT45 offers useful connection options in a slimmer profile than the 60mm UT60 models listed here. Check case clearance and fitting placement before ordering.

White Build Pick – Alphacool NexXxoS UT60 420mm White

For a white-themed build, this UT60 stands out among 420mm radiators for liquid cooling. It measures 468 × 144 × 60mm, supports a triple-140mm-fan layout, and uses copper fins, channels, and chambers.

Best For: White builds with room for a 60mm-thick, triple-140mm radiator.

Pros:

• White exterior suits a coordinated build.
• Six G1/4 ports provide connection options.
• Copper fins, channels, and chambers.

Cons:

• The 60mm thickness needs sufficient case clearance.
• Listed included components specify mounting screws; confirm any other needed fittings separately.

Choose this version if its white finish and port options match your loop plan. Verify radiator and fan clearance before committing to the thicker format.

Oversized Radiator Pick – Alphacool NexXxoS Monsta 420mm

The Alphacool Monsta is a substantial option among 420mm radiators for liquid cooling. Its listed weight of 2,738g makes it a model to plan around, while copper fins, channels, and chambers and three fitting positions per port support a custom-loop installation.

Best For: Builders prepared to check mounting clearance and support for a heavier 420mm radiator.

Pros:

• Copper fins, channels, and chambers.
• Three fitting positions per port.
• Includes five plugs and two lengths of mounting screws.

Cons:

• Its listed 2,738g weight warrants checking case support.
• Supplied notes do not provide dimensions, so verify fit before purchase.

The Monsta makes sense if its weight and port layout work for your case and loop. Confirm the exact dimensions and mounting space rather than relying on the 420mm designation alone.

Black Build Pick – Alphacool NexXxoS UT60 420mm Black

If you want a black-finished option among 420mm radiators for liquid cooling, this UT60 offers a 60mm-thick body for a triple-140mm-fan setup. It measures 468 × 144 × 60mm and has copper fins, channels, and chambers.

Best For: Black builds with clearance for a 60mm-thick 420mm radiator.

Pros:

• Black exterior for a coordinated build.
• Six G1/4 ports and a G1/4 de-aeration plug.
• Includes 30mm and 35mm mounting screws.

Cons:

• Its 60mm thickness can limit installation options in tighter cases.
• One-year manufacturer warranty.

This is the straightforward black UT60 choice when its dimensions and connection layout suit your build. Check clearance with fans installed, not just the radiator’s measurements.

Slim HPE Pick – Alphacool NexXxoS HPE-30 Full Copper 420mm

Among 420mm radiators for liquid cooling, the Alphacool NexXxoS HPE-30 is a full-copper option with G1/4-inch ports and a dedicated fill/drain port. It is worth considering when you want those features in an HPE-30 radiator.

Best For: Custom-loop builders seeking a full-copper 420mm radiator with a fill/drain port.

Pros:

• Full-copper construction includes the water-carrying parts and cooling fins.
• G1/4-inch ports and a fill/drain port provide connection and servicing options.
• Mounting and fan screws are included.

Cons:

• The supplied details do not give exact dimensions, so case clearance needs checking.
• No fan or pump is listed among the included components.

The HPE-30 stands out for its copper construction and included installation hardware. Confirm your case’s 420mm radiator clearance before buying.

X-Flow Pick – Alphacool NexXxos ST30 Full Copper X-Flow 420mm

If you are comparing 420mm radiators for liquid cooling, the Alphacool NexXxos ST30 X-Flow offers a stated 477 x 144 x 30mm footprint and four G1/4-inch threaded ports. Its listed 16 fins per inch and material breakdown make it easier to assess for a planned custom loop.

Best For: Builders who want an X-Flow 420mm radiator with published dimensions and four G1/4-inch ports.

Pros:

• Four G1/4-inch threaded ports.
• Specified 477 x 144 x 30mm dimensions help with fit planning.
• Copper chambers, fins, and channels are listed.

Cons:

• The listed construction also includes steel side panels and brass threads; it is not copper in every component.
• Its 477mm length needs to be checked against case clearance.

This ST30 is a practical choice when its X-Flow layout and port count suit your routing plan. Check the full radiator length, not just its 30mm thickness, before committing.

HPE-45 Pick – Alphacool NexXxoS HPE-45 Full Copper 420mm

The Alphacool NexXxoS HPE-45 is another full-copper choice among 420mm radiators for liquid cooling. It lists G1/4-inch ports, a fill/drain port, and both case and fan mounting screws.

Best For: Builders seeking a full-copper HPE-45 radiator with a fill/drain port and included mounting screws.

Pros:

• Full-copper construction includes the water-carrying parts and cooling fins.
• G1/4-inch ports and a fill/drain port are listed.
• Case and fan mounting screws are included.

Cons:

• The supplied dimensions are identical on all three axes, so they are not useful for confirming radiator clearance.
• No fan or pump is listed among the included components.

Choose the HPE-45 for its stated materials and connection features, but verify the actual physical dimensions with the seller before planning a tight installation.

How We Picked the Best 420mm Radiators for Liquid Cooling

This roundup covers seven Alphacool full-copper models with distinct thicknesses, layouts, or finishes. We organized them around practical buying decisions: where the radiator fits, how much fan space it leaves, and whether its port arrangement suits the planned tubing route. We did not treat thickness alone as a performance ranking; results depend on fan speed, airflow restrictions, coolant flow, and the heat your loop needs to dissipate.

Quick Comparison

Start with clearance. The ST30 X-Flow and HPE-30 are the thinner choices when space is tight. The XT45 and HPE-45 sit in the middle. The UT60 models need more depth and come in black or white, while the Monsta is the thickest option and calls for especially careful fit checks. Choose the ST30 X-Flow if ports at opposite ends help your tubing route; choose a finish only after confirming the physical fit.

Key Buying Factors for 420mm Radiators for Liquid Cooling

Case and Fan Clearance

Confirm that your case supports a 420mm radiator in the intended position—not merely three 140mm fans. Check the manufacturer’s radiator dimensions, mounting-hole pattern, and available clearance against the motherboard, memory, power cables, front panel, and other installed components. Add the thickness of your chosen fans to the radiator depth, then leave room for screw heads and airflow. A top mount can fail on motherboard clearance even when the case lists 420mm support.

Thickness and Airflow

A thicker core offers more surface area, but that does not guarantee a worthwhile gain in every build. Dense or deep radiators can benefit from stronger fans or higher fan speeds, which may increase noise. If quiet operation matters, consider the fans you will actually use and the air they can draw through the case before choosing the deepest model. Radiator space and unobstructed intake air are often more useful than thickness alone.

Ports, Materials, and Installation

Sketch your loop before ordering. Standard and cross-flow port layouts can lead to very different tube paths, particularly in a tight case. Check fitting clearance near panels and fans, and verify port threads and accessory needs against the exact model listing. These are full-copper radiators, so pair them with compatible loop components and coolant; avoid mixing aluminum into a copper-based loop unless the entire system is specifically designed for it. Flush a new radiator according to its manufacturer’s guidance before installation.

Who Should Buy Which 420mm Radiators for Liquid Cooling?

For a constrained build, begin with the HPE-30 or ST30 X-Flow, then decide whether the cross-flow layout simplifies tubing. For a middle-ground depth, compare the XT45 and HPE-45 against your available clearance and fan plan. Pick a UT60 when the case has the room and you want a thicker core; the white and black versions also let you match the build. Reserve the Monsta for a spacious case where radiator-and-fan depth has been measured in advance. Whichever you choose, verified fit is more valuable than buying the largest radiator on the list.