I picked up a 2G Pi 4 yesterday and did some basic thermal testing using the onboard thermal readouts.
None modified Pi 4 running the latest Raspbian will idle at 67C in a room that is 22C.
Pointing a small 30cm 5V fan powered off the GPIO header will reduce this to ~50C.
Placing a heatsink on both the CPU and RAM reduces the temp to 50C.
Modifying a Pi 3 heatsink + fan combo to fit the Pi 4 results in a 42C idle temp.
The life expectancy of the board may be decreased due to the higher idle temp. IMO I would say a heatsink is the bare minimum for running a Pi 4 and a heatsink fan combo is required for anything process intensive such as 4k video.
None modified Pi 4 running the latest Raspbian will idle at 67C in a room that is 22C.
Pointing a small 30cm 5V fan powered off the GPIO header will reduce this to ~50C.
Placing a heatsink on both the CPU and RAM reduces the temp to 50C.
Modifying a Pi 3 heatsink + fan combo to fit the Pi 4 results in a 42C idle temp.
The life expectancy of the board may be decreased due to the higher idle temp. IMO I would say a heatsink is the bare minimum for running a Pi 4 and a heatsink fan combo is required for anything process intensive such as 4k video.