Question Fanless NH-D15S with just case fan—will it work?

[Scoox]

I'm planning to build an ITX case using aluminium profile and carbon fibre board. I'll be using positive pressure air cooling. CPU will be Intel i9-9900K. If I install a single 14cm fan at the front and the case has no holes, cracks or gaps other than the 14cm ø fan inlet and exhaust holes at the rear so the case effectively functions as a duct, would I get away with a fanless Noctua NH-D15 heatsink with its fan used as a case fan? Put another way, what's the difference between having the fan blowing right up against the heatsink vs having it a an inch or two away? The way I see it, air is still going to be forced past the heatsink. I don't intend to overclock BTW.

 

[Darkbreeze]

No possible way you can get away with passive cooling on a 9900k. Not possible. Even with EXTREMELY good active cooling in the form of twin finstack heatsinks with dual fans, or liquid cooling, that CPU still tends to live right at the edge of what's tolerable during stock all core boost operations. Trying to passively cool one, especially with a heatsink that was not designed or intended to SPECIFICALLY be used for passive cooling, is a VERY bad idea.

The difference, is HUGE. An inch away, practically ZERO airflow will pass THROUGH the heatsink. Even when a fan is strapped directly onto the heatsink, you need to have a model with good static pressure characteristics and even then SOME airflow will be lost to reversion leaks or back pressure blowout unless you have a very good fan with good static pressure.

Overclocking has nothing to do with it in this case. That CPU at the stock configuration has a higher thermal design power than most other processors do when overclocked.