Question Fan setup

[Jackrouach]

I have the phanteks evolve mini itx with z390-i mobo and h115i cooler
I currently have 2 140mm fans intake in front and 1 140mm fan intake on back the h115i on top as exchaust was told to have the back intake so not to steal air from the h115i is this good my idles are 34-42c not to happy with that.
I was thinking not enough exhaust but like mentioned above if I set the back to exhaust it makes sense it will steal air from the h115 or no??

 

[Darkbreeze]

34-42°C idle is not bad at all, especially considering the cramped space inside that case AND even more so if you have a fairly decent tiered graphics card adding to it.

Idle temps don't really make any difference to anything anyhow, unless you are not able to remain below the maximum full load temperature. Have you run Prime95 (AVX/AVX2 disabled) to test the full load, steady state maximum temperature and determine if it is staying below 80°C? 85°C would be the absolute maximum we want to see during this test.

Personally, I'd recommend you flip that fan as an exhaust. There is really no such thing as "stealing" from an AIO that is exhausting out of the case anyhow. The worst it could do is create an even lower negative pressure arrangement which favors cooling performance anyhow and just makes it easier for the intake fans to bring even more fresh ambient air into the case.