Convection is the main mantra of passive cooling. With vents on the top (and mesh panels) the Cooler Master Elite 110 will provide enough fresh air for natural convection to occur.
Add a highly capable and hyperthreaded Pentium G5500T (35W TDP), Arctic's Alpine 11 Passive CPU cooler, ASUS H310T Thin mini-ITX motherboard (with DC power), a compatible 150W FSP adapter, 8GB of Crucial memory, a trusty 500GB Samsung SSD, and here's your $450 fanless Coffee Lake PC.
