Originally Posted by Blameless
I'd like to add that when delivering cool intake air isn't always practicable, warm air flow is better than no air flow, and more air flow is better than less. As long as the air flowing over components is cooler than the components involved, the components will be cooled.
This is why a lot of datacenters and other installations are moving from conditioned/chilled air to outside air. It's often cheaper and more effective to push two or three times as much ~40C intake air through hardware than it is to cool a lesser volume of air to just above the dew point.
Clearly, if you have the option to blow cool intake air directly at a component without disturbing airflow through the rest of the case, one should take it, but if not, don't be afraid of air that's exhaust from something else.
40c component intake is about 15c above room.
If that's the best you can get, okay.
I optimize and help others optimize case airflow almost every day, and if we start with a system that is supplying 15-20c air to component we end up being able to low that intake air temp by 5-10c without much effort. It is not hard to get component to <10c .. and attaining 5c is usually not a problem. This is with CPU and GPU at full load.
One of the biggest problem I see is systems with fixed speed case fans .. meaning they supply more air then wanted 68% of the time, and not enough 30% of the time .. with only the right amount 2% of the time. The case's flow paths are changing almost every time the component fans change speed.
Few of us live in environments where our computer rooms are above 28c .. most of us have 20-25c rooms. There is no logical reason to have a system that cannot supply it's components with air less than 10-15c above room ambient. All of mine have less than 8c above ambient component intakes and that 8c one is HTPC that operates at 60c at 100% load.
Warm airlfow may not be better depending how warm 'warm' is.
As often as not three times as much 10c warmer airflow will not cool as well as 66% as as much 5c cooler air does.
Sure, we can operate components at 50c with 40c airflow, or we can operate them at 38c with 28c airflow from a 22c room. It is not really all that hard to select case and components that the case cannot supply components with airflow 4-8c above room ambient .. rather than the 20-34c warmer
hotter component intake air temp resulting in 20-25c hotter components with fans screaming at full speed we often see and hear in poorly setup hard working gaming systems inexperienced people build.
Generally all it takes is 30 minutes of reading the right guides, an inexpensive $5 digital indoor / outdoor wired remote thermometer, and maybe an hour or two of playing around changing fan placement & profiles, and maybe getting a couple fans better suited to the task.