£159.79 inc VAT
The Passiv is built using largely the same components as the Cool Answer III. They both share the same waterblock, pump, reservoir, power plants, and 3/8” tubing diameter. So once again you’ll need to find a spare Molex on your PSU.
Where the two systems differ is in how they expel the CPU’s heat from the case. The Cool Answer uses a large 120mm fan, whilst the Passiv uses a monolithic radiator that you bolt onto one of your case panels.
The radiator itself is made of six aluminium extrusions, each of which is threaded at both ends. The radiator is supposed to be snapped together with brass clips, these require a mallet to attach but when you get them on they hold the assembly together securely.
The radiator is still quite fragile until you manage to screw all the hoses in place along the bottom and top of the assembly. While it may look and sound quite simple, it’s actually a tricky business connecting up the tubes. We found the best method was to make a long string connectors and then screw them all in together, a couple of twists at a time.
When that’s done you need to drill some holes in one of your side panels and bolt the radiator to the side of your case. Surprisingly, the holes in the radiator fins, which you must screw into, aren’t tapped so you’ll need a lot of strength to force the self-tapping screws into the Aluminium. Even though there’s no danger of you screwing so far that you cause a leak, we still recommend you attach the radiator before filling the system with water, as it will be a lot less stressful.
When you finally assemble your radiator you’ll need to connect the hoses from the pump, to the top of the radiator, on to the CPU waterblock and then back to the pump input. All the components are clearly labelled with IN or OUT labels, so connection is quite simple. However the manual recommends that you allow water to flow from the top and exit from the opposite corner.
The kit also comes with some water additive, but you will need to find distilled or deionised water to dilute it with.
Both the Alphacool water kits come with clips to attach the thick copper block to a variety of different CPUs. Unlike some of the other multi-socket clips, the Alphacool doesn’t require you to remove the motherboard. Instead it uses a mounting plate, with standard LGA775 pins and an Allen bolt to create the required mounting pressure for the waterblock to work effectively.
Unlike the Cool Answer, the Passiv doesn’t have a 120mm fan to add to noise levels. Instead the only part of it that produces noise is the tiny Eheim pump. It is perfectly silent – if you can isolate the unit from the case. The kit comes with a slab of Velcro for this purpose, and we found it removed all but a hint of thrumming sound that was transmitted when the pump and reservoir were laid directly on the floor of the case.
When the CPU isn’t under load the Passiv gave the lowest CPU temperature, at 16°C below the Intel reference. The performance under load is much more important, though, and the Passiv didn’t disappoint. Without any active cooling it managed to hold the CPU core 12°C below the temperature of the Intel reference cooler. To make sure that this measurement was accurate we allowed the test to run much longer than any of the air coolers. It took longer than four hours for the system to reach this temperature, and if you need greater performance you could easily blow a desk fan at the exposed radiator.
While it’s by far the most expensive kit on test it’s also the quietest, and possibly the most attractive to look at. The quality of the build and design is excellent, although the radiator is quite difficult to assemble and if you make any mistakes in the construction and testing of the system you stand to fill your case with water.
There’s nothing wrong with its performance either, and it takes hours for the fluid inside the system to reach its maximum temperature.
Assembly and mounting difficulty
Quality and aesthetic