Question How low would TDP need to be to use an AIO with no dedicated fans?

[PB97]

For a novelty custom PC case built as an art project not a practical machine, how low a TDP would you need so that could cool the CPU using an AIO pump and 240mm radiator, but without any dedicated fans?

The fans in the case are two front mounted 120mm fans.

 

[TerryLaze]

It works the other way around, the CPU will use as much TDP as the cooler can provide and will run at according clocks, it will run at its maximum allowed safe temp which at default is 100 C for intel and 95 C for ryzen.

Your question should be how much TDP to reach x y z amount of performance.

 

[Paperdoc]

An AIO system with NO air flow through the rad is almost useless. All of the heat removal is done by the air blowing through the rad and out of the case somehow.

I really do NOT recommend what TerryLaze has written above. That post IS correct - a CPU that is not cooled adequately will continue to operate for some time under very much reduced workload (by reducing drastically the speed of the processor) in order to prevent catastrophic damage to the CPU. It may even stop entirely if there is NO cooling. But working at a high-limit temperature for long periods is sure to shorten its lifetime.

MANY AIO installations place the rad AND its fans at the front of the case so that the rad fans are INTAKE fans for case air flow. They thus replace the front-fans-only layout. The flow room air from those fans cools the rad (and hence the CPU) AND provides slightly warmed air into the entire case for cooling of the rest of your system. Consider mounting the rad and fans this way in place of your existing front intake fans.

 

[PB97]

Maybe a better question should be "how low (in terms of specification) do I need to go before I can passively cool a CPU with just water pumping through a rad".

For example, an old 486, they used to run OK with just a heat sink and no fan?

 

[hotaru.hino]

At best I'd probably say a Core i3 or a Ryzen 3, maybe a Ryzen 5.

The problem is that the fins of the radiator aren't conducive to supporting passive airflow and natural convection is an incredibly slow process.

 

[geofelt]

If you have two front 120mm intake fans and the aio radiator is mounted on top, you should get some cooling.
But, why not look for a cooler designed for passive cooling like the Noctua NH-P1:

NH-P1

The NH-P1 is Noctua’s first passive CPU cooler and has been custom-designed for fanless operation from the ground up: in enclosures with good natural convection, its six heatpipes and thick, widely spaced heatsink fins enable it to cool modern high-end CPUs with low to moderate heat dissipation...

noctua.at