I have a little Intel i5 behind me all year long, and I don't notice any effect on the temperature of this (small) room. 12 watts is not a lot of heat to be dumping.

This is really small fry compared to other HVAC efficiency concerns, and definitely not an issue outside of summertime temps in most locales.

My Threadripper on the other hand - I had to move that into the crawlspace as it was: a) loud as hell, and b) basically a space heater that also does useful compute. 160w idle, ~280w full tilt - that thing is very noticable.

This is exactly why I upgrade my old 2012 server. I was able to cut the power usage (and heat generation) by over 90%.

It makes a big difference in the summer, but I miss it during the winter.